Magnitude Of Eutrophication Research Articles

A Regional Survey of the Extent and Magnitude of Eutrophication in Mediterranean Estuaries of Southern California, USA

The magnitude and extent of eutrophication was assessed at 27 segments in 23 estuaries in the Southern California Bight (SCB) between October 2008 and 2009. We applied thresholds from the existing assessment frameworks from both the European Union and the U.S. National Eutrophication Assessment to measurements of three indicators [macroalgae biomass and cover, phytoplankton biomass, and dissolved oxygen (DO) concentration] to categorize eutrophic condition in each estuary. Based on these frameworks, a large fraction of segments had moderate or worse eutrophic condition—78 % based on macroalgae, 39 % for phytoplankton, and 63 % for DO. Macroalgal biomass exceeding 70 g dw m−2 and 25 % cover was found at 52 % of sites during any sampling event and in 33 % of segments for 8 weeks or longer, a duration found to negatively impact benthic infauna. Duration of hypoxic events (DO < 4 mg L−1) was typically short, with most events less than one day; although 53 % of segments had at least one event longer than 24 h. Assessment frameworks of eutrophic condition are likely to evolve over time as the body of literature on eutrophication grows, including aspects such as the applicability of indicators in specific habitat types, indicator thresholds, and how event frequency and duration are incorporated. This paper informs this debate by discussing how eutrophic conditions in SCB estuaries are categorized using different indicators and thresholds. To this end, categorization of estuarine eutrophic condition was found to be very sensitive to the type of threshold, how data are integrated to represent duration or spatial extent, and how indicators are used as multiple lines of evidence.

Anthropogenic eutrophication shapes the past and present taxonomic composition of hybridizing Daphnia in unproductive lakes

It has been proposed that anthropogenic eutrophication of lakes facilitated the establishment of populations of the cladoceran Daphnia galeata into the originally oligotrophic lakes north of the European Alps in the 1960s. This hypothesis lacks the support of studies on unproductive lakes, in which the past eutrophication is assumed to have never been on the level necessary for D. galeata to reach high abundances and to establish permanently. In order to investigate if such species shifts also happened in unproductive systems, we studied the past and present taxonomic composition of three ultra‐oligotrophic Swiss lakes that were only marginally affected by eutrophication using molecular methods on diapausing eggs sampled from sediment cores. D. galeata temporarily established in unproductive lakes, but its colonization success seemed to depend on the general trophic state of the lake and the magnitude of eutrophication. In two of the studied lakes, D. galeata could establish a significant population size, whereas it was not successful in the most unproductive lake with the weakest eutrophication. Even in unproductive lakes, eutrophication led to partly irreversible species changes, providing evidence that this anthropogenic disturbance is responsible for species shifts in many pre‐alpine lakes in Central Europe.

Nonlinear behavior of the socio-economic dynamics for lake eutrophication control

To succeed in combating lake eutrophication, cooperation of local inhabitants, small factories, and farmers in reducing phosphorus discharge is very important. But the willingness of each player to cooperate would depend on the cooperation of other players and on the level of environmental concern of the society in general. Here we study the integrated dynamics of people's choice of behavior and the magnitude of eutrophication. Assumptions are: there are a number of players who choose between alternative options: a cooperative and environment-oriented option is more costly than the other. The decision of each player is affected by “social pressure” as well as by economical cost of the options. The lake pollution increases with the total phosphorus released, and a high pollution level in the lake would enhance the social pressure. The model includes a positive and a negative feedback loops which create diverse dynamical behavior. The model often shows bistability — having an equilibrium with a high level of cooperation among people and clean water, and the other equilibrium with low cooperation and polluted water, which are simultaneously stable. The model also shows fluctuation between a high and a low levels of cooperation in alternating years, cycle with a longer periodicity, or chaotic fluctuation. Conservatism of people stabilizes the system and sometimes helps maintaining cooperation. The system may show unexpected parameter dependence — the improved phosphorus removing efficiency might make water more polluted if it causes the decline in the environmental concern and cooperation among people.

Assessing Recent Eutrophication in Coastal Waters of the Gulf of Finland (Baltic Sea) using Subfossil Diatoms

Marine eutrophication of estuaries and coastal waters is considered to be a significant problem worldwide. In the semi-enclosed Baltic Sea, where the nutrient load has strongly increased from its natural level, this has led to marked changes in the coastal ecosystems. A key to successful management of coastal waters is reliable scientific evidence of their past state. The palaeolimnological record of subfossil diatoms was used to study the rate and magnitude of eutrophication over the last ca. 200 years in two urban and three rural sites. The urban sites showed marked increases in the percentage abundance of planktonic diatoms (from <50 to ca. 90% and from <5 to ca. 70%) and diatom-inferred total dissolved nitrogen (from <800 to ca. 3000 μg l−1 and from <400 to ca. 800 μg l−1), and a decrease in species richness starting in the 19th – early 20th century with increased urbanisation. At both sites a clear recovery was observed after the cessation of waste water loading by the mid 1980s. The present planktonic diatom assemblages of these embayments, however, show no change back to the pre-disturbance diverse benthic communities. In contrast, the changes observed in the rural sites were only moderate and occurred later starting in the 1940s. No marked increases in diatom-inferred total dissolved nitrogen were seen, however, all sites showed an increase in small planktonic taxa (from ca. 1–6% to 8–36%) indicating increased nutrient enrichment and turbidity. These small floristic changes could be seen as an early warning signal despite little change in the inferred nutrient concentrations. The results have implications for the European Water Framework Directive, which requires European surface waters to be of good ecological status, defined both by biological and chemical quality elements.

Long‐term trends in eutrophication and nutrients in the coastal zone

We used high‐resolution paleoecological records of environmental change to study the rate and magnitude of eutrophication over the last century in two contrasting coastal ecosystems. A multiproxy approach using geochemical and biological indicators and diatom‐based transfer functions provides a long‐term perspective on changes in nutrient concentrations and the corresponding biological and sedimentary responses. In Roskilde Fjord, Denmark, total nitrogen (TN) increased 85% during the last century, with the most rapid increase occurring after the 1950s, corresponding to the postwar increase in N fertilizer use. In Laajalahti Bay, an urban embayment near Helsinki, Finland, total dissolved nitrogen (TDN) increased with growing wastewater inputs and decreased with the remedial actions taken to reduce these discharges. These changes are small relative to the order of magnitude increases in nutrient loading that have occurred in northwestern Europe, where the dissolved inorganic nitrogen (DIN) load has increased more than threefold in certain areas.