Nutrient Pollution

Nutrient pollution can be a human health and/or ecological problem where septic systems are placed near drinking water wells or nutrient-sensitive surface waters.

From: Handbook of Water Purity and Quality , 2009

Effect of Human Land Development on Water Quality

Michael A. Mallin , in Handbook of Water Purity and Quality, 2009

Septic Systems and Nutrient Pollution

Nutrient pollution can be a human health and/or ecological problem where septic systems are placed near drinking water wells or nutrient-sensitive surface waters. In the aerated soil beneath the drainfield, nitrogen in the wastewater is nitrified to nitrate, which moves readily through soils. High concentrations of nitrate build up in groundwater that can exceed the U.S. EPA's and Canadian human health "blue-baby" syndrome standard of 10  mg-N/L. Studies have shown nitrate concentrations well in excess of this standard in groundwater plumes draining septic system drainfields (Cogger, 1988; Cogger et al., 1988; Postma et al., 1992; Robertson et al., 1998). Drinking wells have been contaminated by nitrate from septic systems (Johnson and Kross, 1990) and in Maryland elevated nitrate concentrations in drinking well waters have been positively correlated with the number of septic systems in the area (Lichtenberg and Shapiro, 1997). Under reducing conditions where nitrification is suppressed, elevated ammonia concentrations will occur in septic plumes (Robertson et al., 1998). Although not as mobile in the soil as nitrate, under sandy porous soil and waterlogged conditions, groundwater ammonia plumes may also impact nearby surface waters and increase eutrophication. Where plumes containing high nitrate or ammonium concentrations enter nitrogen-sensitive surface waters, such as coastal lagoons or coastal blackwater streams, algal blooms may be stimulated with associated hypoxia issues (Rabelais, 2002; Mallin et al., 2004). In the Chesapeake Bay, a statistical analysis of factors influencing seagrass bed health in 101 subestuaries (Li et al., 2007) showed that a sharp decline in seagrass coverage occurred where watershed septic system density exceeded 39/km2.

Phosphate in the wastewater plume tends to bind readily to soils and is much less mobile than nitrate (Cogger, 1988). Considerable phosphate sorption occurs in the vadose zone (Robertson et al., 1998). Even so, under sandy soil conditions or conditions where long usage has led to saturation of phosphate sorption capacity in soils, phosphate concentrations exceeding 1.0   mg-P/L in septic system plumes have been documented as far as 70   m from the point of origin (Robertson et al., 1998). For septic systems serving homes or cottages along lake shores, this can be problematic in that it can contribute to algal blooms and the eutrophication of freshwaters. Karst regions and coarse textured soils low in aluminum, calcium, and iron present the biggest risk of phosphate movement and water contamination (US EPA, 2002).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123741929000042

RESOURCES

R. Innes , in Encyclopedia of Energy, Natural Resource, and Environmental Economics, 2013

Abstract

This article discusses the production side of nutrient pollution from agricultural sources, given that farmers' nutrient management practices and environmental discharges cannot be directly monitored and regulated or taxed. Do unpriced environmental impacts of farmers' fertilizer decisions lead to 'overfertilization'? If so, what is the source of the incentive for overfertilization and how can it be corrected? Two types of farmers are considered: (1) crop farmers who choose how, when, and how much commercial fertilizer to apply to their crops and (2) livestock facility operators who manage the manure waste from their livestock, including treatment regimens and applications to surrounding croplands. This article describes how 'overfertilization' can arise despite fixed coefficient (von-Liebig) production technologies that might be expected to produce fixed fertilizer applications to farmlands. Farmer choices on timing and rates of fertilizer application, between organic and chemical fertilizers, and on livestock manure disposal on farmlands proximate to confined animal production facilities, all yield private economic trade-offs and ignored environmental effects that can motivate government price interventions in fertilizer markets (such as chemical fertilizer taxes) and regulation of observable practices that affect nutrient discharges (such as irrigation and waste treatment technologies).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123750679001182

Trophic State and Eutrophication

Walter K. Dodds , Matt R. Whiles , in Freshwater Ecology (Third Edition), 2020

Abstract

Humans have caused global increases in the numbers of lakes negatively impacted by nutrient pollution since the 1900s. Changes in nutrients can alter ecosystem structure and function in all freshwater habitats. Alteration by increased nutrients is termed eutrophication. Anthropogenic actions (cultural eutrophication) or natural conditions can increase nutrient input. In this chapter, we describe how comparisons among aquatic systems define trophic state, the level of ecosystem productivity, and consider problems that may be associated with eutrophication. Next, we examine the linkages among nutrient loading, nutrients, algal biomass, water clarity, and fish production. Finally, we describe methods for controlling eutrophication and present several case studies. Given the large economic costs associated with improvement of water quality, and the large costs associated with negative effects of nutrient enrichment, eutrophication continues to be a very relevant issue in lakes, streams, and wetlands.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128132555000181

Salt Marshes: Their Role in Our Society and Threats Posed to Their Existence

Silvia Giuliani , Luca G. Bellucci , in World Seas: an Environmental Evaluation (Second Edition), 2019

4.3.3 Vegetation Disturbance and Biological Invasion

Vegetation disturbance resulting from species invasions, as described in the previous section, is more likely in salt marshes impacted by nutrient pollution ( Bromberg Gedan et al., 2009). Species diversity lost by nutrient pollution is due to the predominance of one or two autochthonous species over the others, while Whitcraft, Talley, Crooks, Boland, and Gaskin (2007) have documented the invasion by the exotic salt cedar (Tamarix spp.) in western United States salt marshes, converting succulent plant communities <   1   m in stature into woody dominated communities with a 3-m canopy (Fig. 4.9). The increase in vegetation height might have a significant impact in reducing the salt marsh capacity of erosion control (Boorman et al., 1998).

Fig. 4.9

Fig. 4.9. Example of a natural marsh landscape. In the bottom right corner is represented an area invaded by Tamarix spp.

 (Modified from Whitcraft, C. R., Talley, D. M., Crooks, J. A., Boland, J., &amp; Gaskin, J. (2007). Invasion of tamarisk (Tamarix spp.) in a southern California salt marsh. Biological Invasions, 9, 875–879.)

Habitat alterations linked to diversity lost or exotic species invasion have profound effects on ecosystem-wide physical and biological properties. For example, Phragmites australis is less palatable to animal consumers than other marsh plants, and contemporarily reduces aquatic habitat quality by infilling small streams and ponds and raising the marsh platform (Bromberg Gedan et al., 2009).

Another aspect of biological invasion is the introduction (voluntary or not) of alien animal species into salt marsh ecosystems. Similar to plants, invasive animals cause important modifications to the salt marsh environment as a whole, modifying physical conditions and/or food web structures. For instance, the exotic mussel Musculista senhousia, when introduced in salt marsh environments, acts in a way that creates hard substrates in previously soft sediments, diminishing the density of native clams (Bromberg Gedan et al., 2009). Another example is the isopod, Sphaeroma quoyanum, whose intense burrowing can cause erosion at the marsh edge with the subsequent significant loss of marsh area (Bromberg Gedan et al., 2009). However, invasive species are not always harmful, and can return ecological functions lost to human impacts, as described by Bertness and Coverdale (2013): the absence of predators due to overfishing in a New England salt marsh allowed the native herbivorous crab, Sesarma reticulatum, to denude hundreds of hectares of low marsh. The subsequent invasion of the green crab, Carcinus maenas, reduced the presence of S. reticulatum through their eviction from burrows, thus promoting cordgrass recovery.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128050521000048

Nutrient Use and Remineralization

Walter K. Dodds , Matt R. Whiles , in Freshwater Ecology (Third Edition), 2020

Abstract

Nutrients can be critical basal resources in aquatic systems because they often limit primary production or heterotrophic activity. Understanding ecosystem production, nutrient pollution, and interactions among heterotrophs, autotrophs, and their environment requires an elucidation of nutrient dynamics. In this chapter, we discuss how organisms acquire and assimilate nutrients, the relative amounts needed in different systems, availability of nutrients, and the crucial concept of nutrient limitation. How nutrients are made available (recycled) by heterotrophs as the nutrients cycle through the food web of aquatic systems is also discussed. We also cover the ecological ramifications of ratios of nutrients (stoichiometry); as we discussed in Chapter 14, nutrient cycles do not happen in isolation. Organisms need to take nutrients in from the water surrounding them or in food that is consumed (uptake) and then incorporated into organic molecules used for growth (assimilation). Generally, each of these steps requires energy. In animals that ingest food, uptake and assimilation are not the same; animals excrete many parts of food that are used. Loss of nutrients is excretion and more specifically if it is in inorganic form, remineralization (return to the inorganic state). Mineralization, remineralization, and nutrient regeneration are terms that ecologists use interchangeably.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B978012813255500017X

An overview of algal photobioreactors for resource recovery from waste

Surjith Ramasamy , ... Kannan Pakshirajan , in Bioreactors, 2020

13.1 Introduction

Countries such as Germany (293   PJ) and China (295   PJ) produce maximum bioenergy from biogas plants [1] . Ammonium volatilization, nutrient pollution, and sodacity are the main drawbacks of applying anaerobic digestate to agricultural crops. The discharge of wastewater rich in ammonium, phosphate, and other nutrients leads to algal bloom in natural water bodies, which needs to be treated properly. Throughout the world, 20% of all nitrogen and phosphorus are distributed in wastewater [2].

The utilization of fossil fuels in various industrial and transportation sectors has resulted in an unsustainable economy and the emission of greenhouse gases such as CO x , NO x , SOx, etc. Carbon dioxide (CO2) levels may reach up to 45,000   MT by 2040, which would result in major air pollution problems [3], and therefore CO2 sequestration has become of interest. Compared with physicochemical methods, microalgae-based CO2 sequestration is more attractive as the process is low-cost, energy-saving, and devoid of waste disposal problems. The process can be made more economical when it is combined with wastewater treatment to produce biofuel or any value-added products without the use of additional fertilizers and fresh water [4].

In fact, nutrient-rich anaerobic digestate from biogas plants is a major source of water pollution. There are several biotechnology-based methods for transforming and concentrating waste into valuable products including biohydrogen, biogas, and lipids produced from wastewater. Organic acids, methane, and hydrogen are used to make bioplastic, which is a high-value product, while biomass obtained from this process can be used as a single cell protein or biofertilizer [5]. Organisms with high growth rates such as bacteria, microalgae, and certain plants are often used for recovering nutrients and toxic metals from waste streams. Mainly heterotrophic bacteria, phototrophic anaerobic bacteria, algae, and oxygenic photosynthetic bacteria are used for producing such value-added products from different waste streams. Autotrophic organisms and heterotopic bacteria obtain energy and electrons from organics present in wastewater using external oxygen and this tends to produce a lot of sludge. On the other hand, phototrophic anaerobic bacteria use energy from light, nutrients, and electrons from wastewater, whereas phototrophic algae use CO2 as a carbon source. Thus phototrophic algae and bacteria are capable of converting greenhouse gases, CO2, nitrous oxide, and others into value-added compounds such as biomass, carotenoids, lipids, and hydrogen, thereby reducing the carbon footprint with the help of light [6]. Carbohydrate containing biomass is also a highly suitable substrate for producing bioethanol, hydrogen, and methane. The recovery of nutrients by these phototrophic organisms abate air, water, and soil pollution. Whereas atmospheric nitrogen is available in plenty, other micronutrients, for example, phosphorus, potassium, and magnesium from natural sources, are highly limited and, therefore, need to be recovered from waste. For instance, ammonium, nitrate, phosphate, and potassium are commonly found in different wastewaters, anaerobic digesters, and the explosive and fertilizer industries.

Compared with terrestrial plants and agricultural crops for biofuel production, microalgae has distinct advantages including a reduced requirement of land and water and a high lipid content, etc. [7]. Autotrophic organisms in water require a 106:16:1 ratio of carbon/nitrogen/phosphorus (C:N:P), which may vary based on several physicochemical parameters. Microalgae contain a three-times higher nutrient content than terrestrial plants [8] and require 0.04–0.09   kg of N and 0.003–0.015   kg of P to produce 1   kg of biomass. Microalgae are capable of growing on various inorganic and organic carbon sources such as CO2, sodium bicarbonate, sodium carbonate, glucose, acetate, and glycerol.

Open-type wastewater treatment ponds such as facultative ponds are ineffective as compared with closed and well-designed reactor systems. This is due to the fact that the efficiency of open treatment systems depend on external environmental factors such as contamination due to bacteria and other organisms, which cannot be controlled, unlike in a closed system. The product formation, growth rate, and physiochemical characteristics of algae are highly influenced by various abiotic factors such as light intensity, temperature, pH, and mixing rheology [9]. Moreover, the treatment efficiency depends on the concentration of pollutants, light intensity, and temperature [10]. Closed and controlled reactor systems such as tubular, airlift, flat panel, and column reactors yield maximum biomass productivity by providing the optimal conditions required for algal growth; and therefore, bioreactors offer long-term, continuous cultivation of algae from waste substrates. Bioreactor-based cultivation is suitable for long-term, continuous cultivation from waste substrates. In addition, closed photobioreactors are effective in preventing waste and CO2 loss, which tend to maintain uniform cell biomass and growth rate.

For the proper design of photobioreactors, nutrient mass transfer and maximum utilization of photons are of primary concern [11]. Media optimization and system biology approaches are followed to maximize the process efficiency and reduce production costs. Table 13.1 presents different photobioreactors studied for application in wastewater treatment with algae and under different cultivation conditions.

Table 13.1. Different algal photobioreactors studied for wastewater and resource recovery and their operation conditions.

SI. no. Microalgae species Reactor configuration Waste substrate Cultivation conditions Biomass/product productivity Operation conditions Reference
1. Chlorella vulgaris Borosilicate tubular bioreactor Effluent from concentrate I (N/P 0.7) Mixotrophic 195.1   mg SS/L days Light intensity 150   µmol/m2  s [12]
Photoperiod 14:10
12 day incubation
Temperature 20°C±1°C
2 Chlorella zofingiensis 10   L tubular column Mixed biogas slurry and municipal wastewater Mixotrophic 0.28   g/L   day biomass, 96.3   mg/L   day lipid Light intensity [13]
150   µmol/m2  s
Photoperiod 12:12
12 day incubation
Temperature 25°C±1°C
3 Cholorella sorokiniana Airlift photobioreactor Bioindustrial wastewater Mixotrophic 0.023   g   dw/L   day Temperature 25°C±1°C [14]
70 day incubation
Sunlight
5. C. vulgaris Membrane photobioreactor Synthetic municipal wastewater Phototrophic 2   mg/L biomass Light intensity 2000   lux [15]
Hydraulic retention time (HRT) 2   days
6. Scenedesmus obliquus Vertical alveolar flat panel photobioreactor Cattle wastewater Mixotrophic Biomass productivity 213–358   mg/L   day HRT 12   day [16]
Photoperiod 24:0
Light intensity 58   µmol/m2  s
7. C. zofingiensis Tubular bubble column photobioreactor Piggery wastewater Mixotrophic 106.28–296.16   mg/L   day biomass productivity Temperature 25°C±1°C [17]
HRT 10   days
11.85–30.14   mg/L   day Light intensity 230±20   µmol/m2  s
8. Botryococcus braunii Submerged membrane photobioreactor Livestock wastewater Heterotrophic 3500   mg/L HRT 3, 4, and 5 [18]
Days
SRT 16   days
Temperature 25°C±1°C
Light intensity
220   µmol   E/m2  s
10 Halochlorella rubescens Twin Layer photobioreactor Municipal wastewater Mixotrophic Microalgal growth 6.3   g/m2 day HRT 8   days [19]
Light intensity
22–220   µmol/m2  s
11 Euglena sp. Sequencing batch membrane photobioreactor Real secondary effluent wastewater Phototrophic 550   mg/L biomass concentrationLipid content 10.09% Biomass retention time (BRT) 60   days [20]
HRT 2, 4, and 8   days
Light intensity 10,000   lux
12 S. obliquus Airlift tubular photobioreactor Domestic wastewater Mixotrophic Maximum areal productivity 21.76.26±0.3   g SS/m2  day HRT 5   days [21]
20.80±0.22   wt.%
14 Chlorella pyrenoidosa Airlift circulation photobioreactor Anaerobic digested starch processing wastewater Photoautotroph 630   mg/L d biomass productivity Two-phase strategy cultivation [22]
69   mg/L   day lipid productivity Temperature 15°C
Light intensity 60   µmol/m2  s
HRT 3–4   days
Temperature 35°C
Light intensity 220   µmol/m2  s
HRT 6–8   days
15 C. vulgaris Membrane photobioreactor Secondary effluent from domestic wastewater Mixotrophic 1.035–1.524   g/L biomass concentration HRT 2   days [23]
BRT 21.1   days
Light intensity 10.5–112.3   µmol/m2  s
16 Scnedesmus sp. Bubble column photobioreactor Olive mill wastewater Photoautotrophic Biomass productivity HRT 21   days [24]
Heterotrophic 86   mg/L day
Biomass production 0.86-1.4   g/L
17 C. vulgaris Photobioreactor Saline wastewater Photoautotrophic Biomass concentration stage 3 1.0380   mg/L Batch cultivation 20   days [25]
Lipid productivity stage 3 54.25   mg/L   day
40% lipid content
18 C. vulgaris Membrane photobioreactor Sewage Photoautotrophic 39.93   mg/L   day Light intensity 8000   lux [26]
Temperature 25°C±2°C
HRT 2.5   days
19 C. vulgaris Biofilm membrane photobioreactor Secondary effluent Phototrophic Volumetric microalgal production 0.072   g/L   day HRT 2   days [27]
Temperature 25°C–28°C
Light intensity 8000   lux
20 C. sorokiniana Photobioreactor Distillery wastewater Photoautotrophic Biomass concentration 12   g/L HRT 4   days [28]
Temperature 27°C
Light intensity 180   µmol photons/m2s

However, the large-scale application of these photobioreactors is restricted due to a lack in understanding of reactor performance under large-scale conditions. Some closed-type reactors have major drawbacks such as overheating, oxygen accumulation, cell damage due to poor light intensity, and insufficient mixing. Hence this chapter discusses all these aspects for the proper design and application of photobioreactors for algae cultivation on waste substrates and resource recovery.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128212646000139

Remarks

Xiao Hua Wang , Isabel Jalón-Rojas , in Sediment Dynamics of Chinese Muddy Coasts and Estuaries, 2019

In Chapter 6 , Keliang Chen and collaborators describe the climatology, hydrology, geology, and biodiversity of Xiamen Bay and evaluate the impacts of nutrient pollution, reclamation, and dredging. The nutrient input from the Jiulong River has recently increased, leading to eutrophication and frequent red tides that have changed the structure of the plankton community. From 1955, Xiamen Bay has been subject to several engineering works such as dikes and dams in order to increase land resources and port infrastructures. As a consequence, the tidal prism decreased, and so have the current velocity and the sediment-carrying capability. These changes implied siltation problems, water quality degradation, the modification of habitats, and the losses of biodiversity and ecosystem services. In recent years, extensive dredging has been implemented to support the coastal reclamation project. Tides drive the dredging-produced sediment to protection zones of Branchiostoma special and dolphin natural reserve, damaging these ecosystems.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B978012811977800008X

Biodiversity

N. Ishii , in Encyclopedia of the Anthropocene, 2018

Food and Agriculture: How to Increase Output Without Degrading Our Environment?

Food and agriculture's impact on the global commons is extensive. Historically, the expansion of agriculture is a dominant driver of land-use change, nutrient pollution, and biodiversity loss. Currently, 37% of Earth's landmass is used to produce food out of which 12% is dedicated to cropland and 25% is dedicated to grazing lands ( FAO, 2014). Agriculture accounts for 80%–90% of freshwater consumption and 24% of global greenhouse gases—GHG—emissions (FAO, 2014). It also contributes to land degradation through the overuse of fertilizers and pesticides.

Another noteworthy fact of the food and agriculture system is its inefficiency. Despite the fact that 793 million people remain undernourished globally today (FAO, 2015), 32% of globally produced food is lost and wasted (Lipinski et al., 2013). Besides the associated financial losses, this means unnecessary GHG emissions and overuse of water and land.

In addition to the current unsustainable practices, the food system faces an exponential challenge to keep up with the increasing demands of a rapidly growing population. Furthermore, as the middle class expands, thriving societies are likely to consume greater quantities of resource-intensive foods like red meat and dairy products. Both of these trends will drive the agricultural system to augment exponentially. According to the World Resources Institute, the food available globally—measured in calories—will need to increase 69% (World Resources Institute, 2013) to feed 9.6 billion people in 2050. If the agricultural practices remain as "business as usual," the impact on the global environment could be extremely harming.

The challenge ahead for the food and agriculture system is to shift to solutions that will increase the global agricultural output without degrading the global environment. This article argues that multistakeholder supply chain approaches, dietary changes, and climate smart agricultural techniques can catalyze change in the food and agriculture system.

Agricultural commodities such as soy, beef, and palm oil are the largest driver for the tropical deforestation, which in turn is a significant part of GHG emissions. Accordingly, how to introduce and mainstream the sustainable farming practices to those commodity production is critical. The key is to bring all relevant actors along the supply chain of individual commodities—from small holders to large plantations, processors, traders, brand and consumers, financiers, and governments—and create incentive systems toward sustainable production and consumption for each of commodities. The role of governments, both national and local, is critical to create a conducive environment, as well as to impose penalties for noncompliance actors.

There are already a number of initiatives for major commodities and their home for production. The Roundtable on Sustainable Palm Oil, Tropical Forest Alliance, and Consumer Goods Forum are among the existing platforms influencing supply chain actors, to work toward diverting the frontier for commodities away from primary forests and areas of high conservation value.

The potential contribution by the GEF is to identify the weakest link of supply chain—in many cases it is small holders in transition to sustainable farming practices—and to strengthen it.

We can argue that dietary switches can have significant impact on the food and agriculture system. Redefining what we eat can contribute greatly to the health of the environment and also in the health of human populations. Ironically we live in a world where famine, hunger, and malnutrition coexist with obesity, diabetes, and food-loss and waste. By providing compelling, attractive, and simple educational messages, governments in partnership with dietary experts and healthy life-style champions could design effective, education campaigns to explain the negative impact of overconsumption of animal protein and other resource-intense food. These nudges can be particularly strong leverage points to spark behavioral changes as we have seen with Michael Bloomberg's antisoda ad campaign in New York City. Additionally, initiatives like FReSH by the World Business Council for Sustainable Development—WBCSD—and EAT Forum are also looking the food system from this perspective.

Due to the increasing changes in climate patterns, the food and agriculture system needs also to adapt to become more productive, resource efficient, and more resilient. Particularly, in countries that still face complex food insecurity challenges. Climate change is already having an impact on reduction of production and lower incomes in vulnerable areas, creating a larger effect on global food prices (FAO, 2013). In order to adapt to the risks associated with the unpredictability of weather patterns and increasing extreme weather events, the transition to climate smart agricultural practices will require a shift in the way land, water, soil nutrients, and genetic resources are managed to ensure that these resources are used more efficiently. This transformation will require considerable changes in national and local governance, legislation, and financial mechanisms. Particularly, small-scale producers need access to technologies and financial services that facilitate the transition to more productive and resilient practices. For instance, technology solutions, such as microirrigation and precision agriculture, are showing new possibilities to use natural resources, like water and land, more efficiently.

By partnering with a diverse range of actors, the GEF is committed to join and strengthen multistakeholder platforms by eliminating the barriers and strengthening the links between actors and their roles. The GEF can help national governments in developing the right policy frameworks to enhance collaboration and long-term planning. Also, the GEF investments can be used to reduce-risk in operations or even to assume the aggregation costs associated with building platforms.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128096659098657

Defining Multiple Stressor Implications

Sergi Sabater , ... Ralf Ludwig , in Multiple Stressors in River Ecosystems, 2019

1.6 Ecosystem Responses to Multiple Stressors

The ecological effects of anthropogenic stressors depend, among others, on the intensity and duration of the stress. Short, low-magnitude effects, such as a short event of moderate nutrient pollution, can produce little changes in the communities because most species are adapted to withstand these changes. Furthermore, the changes tend to be transient, and the community can recover quickly after cessation of the disturbance. However, persistent disturbances can exert stronger effects, leading to structural simplification of the community. High-intensity disturbances can cause strong mortality, but the recovery of the community depends on factors such as the availability of refugia.

The sensitivity of organisms to a given stressor is largely determined by their physiological or ecological properties, of which traits can be used as a proxy. Physiological traits include characteristics such as the ability for detoxification or the capacity for osmotic regulation, whereas ecological traits include characteristics such as feeding types, reproductive strategies, or life histories. The presence or lack of these traits defines the potential resistance of an organism to a given stressor. Some traits, such as living in the water column or onto the water surface, make a difference in the exposure risk to a pollutant in water, for instance. Some other traits, such as the respiration mode (e.g., aerial, through gills, through the tegument, etc.) determine the resistance of organisms to anoxia (Dolédec and Statzner, 2010).

Other factors also modulate the potential response to a stressor. Habitat heterogeneity may increase resistance and resilience to stressors by facilitating refugia to organisms. In large floodplains of high-gradient rivers, for instance, the harsh natural conditions imposed by high-energy flows and sediment mobility may be further impaired by human-driven stressors (e.g., river fragmentation, hydraulic stress, or introduced species; Tockner et al., 2010). In these cases, some periods of low flow become windows of opportunity for the recovery of biological communities, facilitating their resistance to some of these anthropogenic stressors. The windows of opportunity may be environmental opportunities within the physical template of the system, when organisms may recover more easily than during periods of harsher conditions.

On the other hand, repeated or intense disturbances may cause ecological surprises; that is, sudden shifts of the ecosystem to a new ecological state (Paine et al., 1998). In these situations the recurrence of disturbances hampers the possibilities of recovery. The ecosystems carrying capacity (Posthuma et al., 2014) to stressors is challenged by the simultaneous occurrence of multiple stressors. This may take the system beyond its own resistance and resilience capacities, at which time an abrupt change occurs (Groffman et al., 2006). Beyond that tipping point or threshold the ecosystem may exhibit a second, alternative "stable" state, depending on the environmental conditions (Holling, 1973). Scheffer et al. (2012) predicted a higher frequency of critical transitions in highly connected physical and chemical networks, with low heterogeneity among their components. This description closely matches the organization of a river system, and according to these theoretical descriptions the collapse of a given state is plausible, opening a critical transition towards a subsequent state. Long-term data may allow the detection of patterns in ecosystems resulting from multiple stressors (Dodds et al., 2012). As an example, large reservoirs in the lower Ebro River promoted deep changes in the sections upstream and downstream from them; the phytoplankton-dominated community in the lower Ebro during the 1990s (Sabater and Muñoz, 1990) has been substituted by a macrophyte-dominated community (Ibánez et al., 2008).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128117132000017

Innovative Sensor Carriers for Cost-Effective Global Ocean Sampling

Oscar Schofield , ... Aníbal C. Matos , in Challenges and Innovations in Ocean In Situ Sensors, 2019

5.1.1 The Need

Understanding of the oceans' physical–chemical–biological variability, their respective feedbacks, and the responses to anthropogenic forcing (climate change, resource extraction and utilization, waste production, and nutrient pollution), remains a fundamental challenge for oceanography. Our lack of understanding limits our ability to predict future trajectories of the ocean in the face of accelerating change. To meet this challenge, oceanographers need to maintain a sustained presence in the ocean to measure not only the mean state of the system but also the high-frequency changes that can have disproportionately large effects on physics, biology, and chemistry. This requires a range of new approaches for platforms that are capable of carrying a range of sensors as ships cannot provide the needed cost‐effective sustained presence that is required.

Fortunately, oceanographic technologies have been undergoing a technical revolution as autonomous underwater vehicles (AUVs) have matured and are becoming reliable tools to collect data for sustained periods of time. The range of AUVs is maturing rapidly and all of them are tuned to sample specific time and space domains [1]. One particular useful technology is the underwater buoyancy-driven glider. These systems are optimized to collect data over regional scales (100s–1000s of kilometers) and maintain a long-term mobile adaptive sampling presence in the subsurface ocean over ecologically relevant scales. A range of buoyancy gliders [2–5] currently exists and have strong track records for studying a wide range of science topics [6]. All the major gliders used today (Seaglider, Spray, Slocum, and Sea Explorer) have demonstrated great potential; however, for this chapter we will focus on the Slocum glider, which is the system that we have the greatest experience operating [5,7]. This chapter will provide an overview of glider technology, our experience using the platform, and the current range of sensors they have been demonstrated to successfully carry.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128098868000053