SUMMARY 1. This synthesis examines 35 long-term (5–35 years, mean: 16 years) lake re-oligotrophication studies. It covers lakes ranging from shallow (mean depth <5 m and/or polymictic) to deep (mean depth up to 177 m), oligotrophic to hypertrophic (summer mean total phosphorus concentration from 7.5 to 3500 l gL )1 before loading reduction), subtropical to temperate (latitude: 28–65� ), and lowland to upland (altitude: 0–481 m). Shallow northtemperate lakes were most abundant. 2. Reduction of external total phosphorus (TP) loading resulted in lower in-lake TP concentration, lower chlorophyll a (chl a) concentration and higher Secchi depth in most lakes. Internal loading delayed the recovery, but in most lakes a new equilibrium for TP

https://www.uibk.ac.at/limno/files/pdf/jeppesen-et-al.pdf

Lake responses to reduced nutrient loading - an analysis of contemporary long-term data from 35 case studies

As human populations increase and land-use intensifies, toxic and unsightly nuisance blooms of algae are becoming larger and more frequent in freshwater lakes. In most cases, the blooms are predominantly blue-green algae (Cyanobacteria), which are favored by low ratios of nitrogen to phosphorus. In the past half century, aquatic scientists have devoted much effort to understanding the causes of such blooms and how they can be prevented or reduced. Here we review the evidence, finding that numerous long-term studies of lake ecosystems in Europe and North America show that controlling algal blooms and other symptoms of eutrophication depends on reducing inputs of a single nutrient: phosphorus. In contrast, small-scale experiments of short duration, where nutrients are added rather than removed, often give spurious and confusing results that bear little relevance to solving the problem of cyanobacteria blooms in lakes.

http://pubs.acs.org/doi/pdf/10.1021/acs.est.6b02204

Reducing Phosphorus to Curb Lake Eutrophication is a Success

The management of eutrophication has been impeded by reliance on short-term experimental additions of nutrients to bottles and mesocosms. These measures of proximate nutrient limitation fail to account for the gradual changes in biogeochemical nutrient cycles and nutrient fluxes from sediments, and succession of communities that are important components of whole-ecosystem responses. Erroneous assumptions about ecosystem processes and lack of accounting for hysteresis during lake recovery have further confused management of eutrophication. I conclude that long-term, whole-ecosystem experiments and case histories of lake recovery provide the only reliable evidence for policies to reduce eutrophication. The only method that has had proven success in reducing the eutrophication of lakes is reducing input of phosphorus. There are no case histories or long-term ecosystem-scale experiments to support recent claims that to reduce eutrophication of lakes, nitrogen must be controlled instead of or in addition to phosphorus. Before expensive policies to reduce nitrogen input are implemented, they require ecosystem-scale verification. The recent claim that the ‘phosphorus paradigm’ for recovering lakes from eutrophication has been ‘eroded’ has no basis. Instead, the case for phosphorus control has been strengthened by numerous case histories and large-scale experiments spanning several decades.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2012.1032

The dilemma of controlling cultural eutrophication of lakes.

Models of population dynamics in which per capita reproductive success declines at low population levels (variously known as depensation, the Allee effect, and inverse density-dependence) predict that populations can have multiple equilibria and may suddenly shift from one equilibrium to another. If such depensatory dynamics exist, reduced mortality may be insufficient to allow recovery of a population after abundance has been severely reduced by harvesting. Estimates of spawner abundance and number of surviving progeny for 128 fish stocks indicated only 3 stocks with significant depensation. Estimates of the statistical power of the tests strengthen the conclusion that depensatory dynamics are not apparent for fish populations at the levels studied.

https://science.sciencemag.org/content/sci/269/5227/1106.full.pdf

Population Dynamics of Exploited Fish Stocks at Low Population Levels

A review of water quality concerns in livestock farming areas.

Little is known about the recovery of lakes from eutrophication, especially as it effects the cycling of nutrients other than phosphorus. We fertilized a naturally oligotrophic lake (Lake 303) in t...

D. W. Schindler

Papers

Phosphorus, Nitrogen, and Carbon Dynamics of Experimental Lake 303 during Recovery from Eutrophication