Tag Archives: eutrophication

Resilience Theory in Colombia

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Does resilience thinking have any impact at all on the ground? These two very interesting examples came in via Lorena Franco Vidal at the NGO Fundación Humedales de Colombia. In January of this year, the mentioned NGO decided to initiate a climate vulnerability and resilience assessment of the Fúquene wetland complex in the east of the Colombian Andes (2,600 meters over the sea level).

According to Lorena, this work has been very much inspired by a range of publications on “the problem of fit” – that is when the dynamics of complex social-ecological systems isn’t matched by institutions and governance [e.g. Cummings et al 2006, Galaz et al 2008], as well as the Resilience Alliance workbook for scientists. In addition, the evaluation of biochemichal variables (in bottom and water sediments of the lake) are – inspired by Elinor Ostrom’s work – done by the fishermen community of the wetland. According to Lorena, this group of local stakeholders have been training monitoring for 2 years to be able to follow environmental change in the lake system.

But there is more. During 2008 and 2009, papers on “the problem of fit” as well as David Salt’s and Brian Walker’s book “Resilience Thinking”, inspired a suggested reframing of Colombian biodiversity policy towards an increased emphasis on social-ecological systems, and the need to address multilevel interactions in governance. Results of the suggested modification include, amongst other things: i) a new conceptual framework for biodiversity management, based upon the resilience thinking paradigm applied to socio-ecological systems; ii) a model that accounts for the various stability domains in which natural and social systems appear in the territory; and iii) a revision of the state – pressure – response model, in order to include new drivers of change affecting biodiversity.

The outcomes of this latter “update”, are now being used for systematic country-side consultations, and we look forward to hear more from both these initiatives!

Nitrogen deposition making lakes more regulated by phosphorus

Nitrogen deposition is increased the extent to which lake algal populations are regulated by phosphorus, shifting lake food webs.  Because, the patterns of human amplification of nitrogen and phosphorus trasport are different this should drive different patterns in lakes in different regions.

James Elser and other write in Science Shifts in Lake N:P Stoichiometry and Nutrient Limitation Driven by Atmospheric Nitrogen Deposition (2009 326 (5954):835).  From the abstract:

Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden, and Colorado, United States, and, as a result, patterns of ecological nutrient limitation were shifted. Under low N deposition, phytoplankton growth is generally N-limited; however, in high–N deposition lakes, phytoplankton growth is consistently P-limited.

They conclude:

Our findings show that, despite the potential of watershed vegetation uptake and sediment denitrification to buffer lakes against elevated N loading, increased inputs of anthropogenic N have accumulated in receiving waters. As a result, shifts in lake N:P stoichiometry have altered ecological nutrient limitation of phytoplankton growth. Phytoplankton in lakes that are less influenced by anthropogenic inputs experience relatively balanced or N-deficient nutrient supplies, but enhanced N inputs from the atmosphere during the past several decades of human industrialization and population expansion appear to have produced regional phytoplankton P limitation.

Producer diversity is likely to be low when resource supply ratios are skewed in favor of one particular nutrient relative to others (11, 18). Thus, increased N loading from the atmosphere may reduce lake phytoplankton biodiversity, similar to anticipated effects of N deposition on plant diversity in terrestrial ecosystems (19, 20), by possibly favoring those relatively few species that are best able to compete for the limiting P.

… Thus, sustained N deposition that generates stoichiometric imbalance between P-limited, low-P phytoplankton and their P-rich zooplankton consumers (12) may result in reduced production of higher trophic levels, such as fish. Projected increases in global atmospheric N transport during the coming decades (24) are likely to substantially influence the ecology of lake food webs, even in lakes far from direct human disturbance.

Dead Ahead: Similar Early Warning Signals of Change in Climate, Ecosystems, Financial Markets, Human Health

What do abrupt changes in ocean circulation and Earth’s climate, shifts in wildlife populations and ecosystems, the global finance market and its system-wide crashes, and asthma attacks and epileptic seizures have in common?

According to a paper published this week in the journal Nature, all share generic early-warning signals that indicate a critical threshold of change dead ahead. Cheryl Dybas writing for NSF.gov covers a new paper on “Early Warning Signals for Critical Transitions” (Nature, 3 Sept 2009, 461: 53-59).

In the paper, Martin Scheffer of Wageningen University in The Netherlands and co-authors found that similar symptoms occur in many systems as they approach a critical state of transition.

“It’s increasingly clear that many complex systems have critical thresholds–’tipping points’–at which these systems shift abruptly from one state to another,” write the scientists in their paper.

Especially relevant, they discovered, is that “catastrophic bifurcations,” a diverging of the ways, propel a system toward a new state once a certain threshold is exceeded.

Like Robert Frost’s well-known poem about two paths diverging in a wood, a system follows a trail for so long, then often comes to a switchpoint at which it will strike out in a completely new direction.

That system may be as tiny as the alveoli in human lungs or as large as global climate.

“These are compelling insights into the transitions in human and natural systems,” says Henry Gholz, program director in the National Science Foundation (NSF)’s Division of Environmental Biology, which supported the research along with NSF’s Division of Ocean Sciences.

“The information comes at a critical time–a time when Earth’s and, our fragility, have been highlighted by global financial collapses, debates over health care reform, and concern about rapid change in climate and ecological systems.”

It all comes down to what scientists call “squealing,” or “variance amplification near critical points,” when a system moves back and forth between two states.

“A system may shift permanently to an altered state if an underlying slow change in conditions persists, moving it to a new situation,” says Carpenter.

Eutrophication in lakes, shifts in climate, and epileptic seizures all are preceded by squealing.

Squealing, for example, announced the impending abrupt end of Earth’s Younger Dryas cold period some 12,000 years ago, the scientists believe. The later part of this episode alternated between a cold mode and a warm mode. The Younger Dryas eventually ended in a sharp shift to the relatively warm and stable conditions of the Holocene epoch.

The increasing climate variability of recent times, state the paper’s authors, may be interpreted as a signal that the near-term future could bring a transition from glacial and interglacial oscillations to a new state–one with permanent Northern Hemisphere glaciation in Earth’s mid-latitudes.

In ecology, stable states separated by critical thresholds of change occur in ecosystems from rangelands to oceans, says Carpenter.

The way in which plants stop growing during a drought is an example. At a certain point, fields become deserts, and no amount of rain will bring vegetation back to life. Before this transition, plant life peters out, disappearing in patches until nothing but dry-as-bones land is left.

Early-warning signals are also found in exploited fish stocks. Harvesting leads to increased fluctuations in fish populations. Fish are eventually driven toward a transition to a cyclic or chaotic state.

Humans aren’t exempt from abrupt transitions. Epileptic seizures and asthma attacks are cases in point. Our lungs can show a pattern of bronchoconstriction that may be the prelude to dangerous respiratory failure, and which resembles the pattern of collapsing land vegetation during a drought.

Epileptic seizures happen when neighboring neural cells all start firing in synchrony. Minutes before a seizure, a certain variance occurs in the electrical signals recorded in an EEG.

Shifts in financial markets also have early warnings. Stock market events are heralded by increased trading volatility. Correlation among returns to stocks in a falling market and patterns in options prices may serve as early-warning indicators.

“In systems in which we can observe transitions repeatedly,” write the scientists, “such as lakes, ranges or fields, and such as human physiology, we may discover where the thresholds are.

“If we have reason to suspect the possibility of a critical transition, early-warning signals may be a significant step forward in judging whether the probability of an event is increasing.”

Co-authors of the paper are William Brock and Steve Carpenter of the University of Wisconsin-Madison, Jordi Bascompte and Egbert van Nes of the Consejo Superior de Investigaciones Scientificas, Sevilla, Spain; Victor Brovkin of the Max Planck Institute for Meteorology in Hamburg, Germany; Vasilis Dakos of the Potsdam Institute for Climate Research in Potsdam, Germany; Max Rietkerk of Utrecht University in The Netherlands; and George Sugihara of Scripps Institution of Oceanography in California.

The research was funded by the Institute Para Limes and the South American Institute for Resilience and Sustainability Studies, as well as the Netherlands Organization of Scientific Research, the European Science Foundation, and the U.S. National Science Foundation, among others.

Algal Bloom along the Coast of China

There has been a lot of news coverage of the large coastal algal bloom at China’s Olympic sailing site in Qingdao. The Chinese government claims the bloom is now under control.

NASA’s Earth Observatory has published some remote sensed images of the bloom from MODIS:
MODIS comparison of algal bloom

On June 28, 2008, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured these images of Qingdao and the bay of Jiaozhou Wan. The top image is a natural-color image similar to what a digital camera would photograph. The bottom image is a false-color image made from a combination of light visible to human eyes and infrared light our eyes cannot see. In this image, vegetation appears vibrant green, including the strips of algae floating in the bay and in the nearby coastal waters.

These images show the bay at the beginning of a local cleanup effort. (Daily images of the area are available from the MODIS Rapid Response Team.)

Regime shifts in the Gulf of Mexico

Regime shifts in the Gulf of MexicoEugene Turner, Nancy Rabalais, and Dubravko Justic‘s recent article Gulf of Mexico Hypoxia: Alternate States and a Legacy (Env. Sci. Tech., 2008 42(7) 23232327) suggests that benthic carbon in the coastal benthic may be a critical slow variable regulating coastal hypoxia. As organic matter accumulates in sediments it demands increasing amounts of oxygen, making the area more vulnerable to nutrient driven hypoxia.

The Gulf of Mexico is one of the most studied coastal hypoxic zones in the world, but it is not the only one. The number of these zones has greatly increased, primarily due to agricultural expansion and intensification (one of the many ways that agriculture has been driving ecological regime shifts). The authors compare changes in coastal hypoxia in the Gulf of Mexico to that found in the Baltic Sea, which has also been suggested to have undergone a regime shift. The authors conclude:

… there has been a system-wide response to the combination of organic buildup in the sediments and higher nitrogen loading, which has increased the area of hypoxia generated for a given nitrogen load and has increased the opportunity for hypoxia to develop. The results discussed above demonstrate that the average [nitrogen] loading of the 1980s would result in a hypoxic zone that is twice as large in the past decade.

…Hypoxia has well-documented catastrophic consequences to the benthos, including animals with multiyear life spans, and creates large areas without commercial quantities of shrimp and fish. The changes in the Mississippi River-influenced continental shelf over the last 30–40 years should be considered to a shift to an alternate state in the sense that (A) the threshold for hypoxia development has been exceeded on a continuing basis and the size of the hypoxic zone has increased and may be approaching its maximum size, given physical constraints on shelf geometry (e.g., width, depth, and length); and (B) the return to a previous system state is more difficult the longer that the current level of nutrient loading is stable or increasing.

… respiratory demand in the sediments remains a legacy influencing water quality of the eutrophied continental shelf in the northern Gulf of Mexico. …The goal of reducing the size of the hypoxic zone to 5000 km2 thus becomes more difficult to achieve for every year without a significant reduction in nutrient loading. Each year without reducing the nutrient loading rates means that it will take longer to realize the Action Plan goal, because the legacy of accumulated organic matter and its respiratory demand increases with time.

Climate change amplifies eutrophication

Hans Paerl and Jef Huisman have a perspective article in Science that reviews how climate change may promote blooms of cyanobacteria Blooms Like It Hot (320 (5872): 57 ):

Nutrient overenrichment of waters by urban, agricultural, and industrial development has promoted the growth of cyanobacteria as harmful algal blooms (1, 2). These blooms increase the turbidity of aquatic ecosystems, smothering aquatic plants and thereby suppressing important invertebrate and fish habitats. Die-off of blooms may deplete oxygen, killing fish. Some cyanobacteria produce toxins, which can cause serious and occasionally fatal human liver, digestive, neurological, and skin diseases (1-4). Cyanobacterial blooms thus threaten many aquatic ecosystems, including Lake Victoria in Africa, Lake Erie in North America, Lake Taihu in China, and the Baltic Sea in Europe (3-6). Climate change is a potent catalyst for the further expansion of these blooms.

Rising temperatures favor cyanobacteria in several ways. Cyanobacteria generally grow better at higher temperatures (often above 25°C) than do other phytoplankton species such as diatoms and green algae (7, 8). This gives cyanobacteria a competitive advantage at elevated temperatures (8, 9). Warming of surface waters also strengthens the vertical stratification of lakes, reducing vertical mixing. Furthermore, global warming causes lakes to stratify earlier in spring and destratify later in autumn, which lengthens optimal growth periods. Many cyanobacteria exploit these stratified conditions by forming intracellular gas vesicles, which make the cells buoyant. Buoyant cyanobacteria float upward when mixing is weak and accumulate in dense surface blooms (1, 2, 7) (see the figure). These surface blooms shade underlying nonbuoyant phytoplankton, thus suppressing their opponents through competition for light (8). Cyanobacterial blooms may even locally increase water temperatures through the intense absorption of light. The temperatures of surface blooms in the Baltic Sea and in Lake IJsselmeer, Netherlands, can be at least 1.5°C above those of ambient waters (10, 11). This positive feedback provides additional competitive dominance of buoyant cyanobacteria over nonbuoyant phytoplankton.

Global warming also affects patterns of precipitation and drought. These changes in the hydrological cycle could further enhance cyanobacterial dominance. For example, more intense precipitation will increase surface and groundwater nutrient discharge into water bodies. In the short term, freshwater discharge may prevent blooms by flushing. However, as the discharge subsides and water residence time increases as a result of drought, nutrient loads will be captured, eventually promoting blooms. This scenario takes place when elevated winter-spring rainfall and flushing events are followed by protracted periods of summer drought. This sequence of events has triggered massive algal blooms in aquatic ecosystems serving critical drinking water, fishery, and recreational needs. Attempts to control fluctuations in the discharge of rivers and lakes by means of dams and sluices may increase residence time, further aggravating cyanobacteria-related ecological and human health problems.

Nitrogen transfer from sea to land via commercial fisheries

Roxanne Maranger an ecologist at the University of Montreal and other have a neat paper in Nature Geoscience Nitrogen transfer from sea to land via commercial fisheries that shows that commercial fishing removed substantial amounts of nitrogen from coastal oceans. They show that while fertilizer run-off into the ocean and fishery removal of nitrogen have increased over the past forty years, the increase in nitrogen inputs has been faster. Consequently the proportion of nitrogen removed from coastal zone has dropped from a global average of about 60% in 1960 to about 20% in 2000. This trend as well as the spatial pattern of nitrogen withdrawal are shown in figure 1 of their paper:

Nature GeoScience

Figure 1. a, Total amount of N in fertilizer run-off (Tg N yr-1=1012 g N yr-1) delivered to the global ocean (left axis, blue line) and N returned as fish biomass (left axis, red line) per year over time. The orange line (right axis) is the proportion of fish N removed relative to fertilizer N exported (ratio fish N:fertilizer N) reported as a percentage. b, The ratio of fish N removed to fertilizer N entering 58 different large marine ecosystems (LMEs) for the year 1995.

The paper shows that fishing can help reduce the impacts of nitrogen pollution. But that nitrogen pollution that destroys fisheries, through the creation of anoxic “dead zones”, can make nitrogen pollution even worse by removing a major source of nitrogen withdrawals. Similarly, overfishing the reduces the amount of fish biomass that can be removed from a system will make the system more vulnerable to eutrophication.

Mapping Coastal Eutrophication

Current industrial agricultural practices produce a tradeoff between agricultural production and the quality of coastal ecosystems, because agricultural fertilizers that increase crop yields lead to the creation of low oxygen hypoxic areas in areas which receive a lot of nutrient rich runoff.

The World Resources Institute and Virginia Institute of Marine Science, has updated Diaz et al’s recent map of coastal eutrophication. They identify 169 hypoxic areas, 233 areas of concern, and 13 systems in recovery.

Coastal Eutrophication WRI 2008

The WRI Earthtrends weblog writes about the project:

The map shows three types of eutrophic zones:

(1) Documented hypoxic areas – Areas with scientific evidence that hypoxia was caused, at least in part, by an overabundance of nitrogen and phosphorus. Hypoxic areas have oxygen levels low enough to inhibit the existence of marine life.

(2) Areas of concern – Systems that exhibit effects of eutrophication, including elevated nitrogen and phosphorus levels, elevated chlorophyll levels, harmful algal blooms, changes in the benthic community, damage to coral reefs, and fish kills. These systems are impaired by nutrients and are possibly at risk of developing hypoxia. Some of the systems may already be experiencing hypoxia, but lack conclusive scientific evidence of the condition.

(3) Systems in recovery – Areas that once exhibited low dissolved oxygen levels and hypoxia, but are now improving. For example, the Black Sea recovery is largely due to the economic collapse of Eastern Europe in the 1990s, which greatly reduced fertilizer use. Others, like Boston Harbor in the United States and the Mersey Estuary in the United Kingdom also have improved water quality resulting from better industrial and wastewater controls.

Given the state of global data, the actual number of eutrophic and hypoxic areas around the world is likely to be greater than the 415 listed here. The most under-represented region is Asia. Asia has relatively few documented eutrophic and hypoxic areas despite large increases in intensive farming methods, industrial development, and population growth over the past 20 years. Africa, South America, and the Caribbean also have few reliable sources of coastal water quality data.

A more detailed analysis of this data set will be available in February 2008 in a policy note entitled Eutrophication and Hypoxia in Coastal Areas: A Global Assessment of the State of Knowledge (a list of related publications can be found here.

Mapping anoxic zones – pt 2

Global International Waters Assessment is a systematic assessment of the environmental conditions and problems in large transboundary waters, comprising marine, coastal and freshwater areas, and surface waters as well as ground waters. Involving over 1,500 expert it has assessed 66 of the world’s major river basins and recently published a synthesis report. These publications are freely available online. The synthesis report‘s section on pollution provides a map of eutrophication impact.

Fig 14 GIWA

As mentioned in a earlier post on mapping dead zones, eutrophication can produce large coastal hypoxic zones. The GIWA regional assessments reported that dead zones:

… have become increasingly common in the world’s lakes, estuaries and coastal zones, with serious impacts on local fisheries, biodiversity and ecosystem functions. Extensive dead zones have been observed for many years in the Baltic Sea, Black Sea and Gulf of Mexico. The GIWA assessment has compiled information on dead zones in the Southern Hemisphere, including several lagoons in the Brazil Current region, coastal locations in the Humboldt Current region, and in the Yangtze River estuary located in the East China Sea region.