Nutrient chemistry and eutrophication risk assessment of the Ghaghara River, India

This study was carried out to evaluate the eutrophication risk associated with the nutrient flux from the Ghaghara river by using nutrient molar ratios and indicators for coastal eutrophication potential values. The concentration of ammonium (3–8 times), nitrate (3–10 times), and phosphate (3–4.5 times) in the Ghaghara river were higher than the reported value for the unpolluted rivers indicating the contribution from the anthropogenic sources. The dissolved nutrients concentration showed significant seasonal variations in the Ghaghara river system. The specific yield of nitrate-N, phosphate-P, and dissolved silica-Si from the Ghaghara river were 0.49, 0.03 and 0.96 tons km−2 yr−1 respectively. The average molar ratio for dissolved inorganic nitrogen (DIN)/Dissolved inorganic Phosphate (DIP) was above 16:1, indicated phosphate limitation in biological productivity. In contrast, an average molar ratio of Dissolved inorganic Silica (DSi)/DIN of 4.6 ± 4.4 favored the diatom growth in the Ghaghara river. The negative value of P-ICEP (-2.93 kg C. km−2day−1) indicated phosphate limitation in the Ghaghara river. The positive value of N-ICEP (1.71 kg C·km−2day−1) indicates an excess of nitrogen over silica transport from the Ghaghara river to the Ganga river, which can create an eutrophication problem in the Ganga river.

The Complicated and Confusing Ecology of Microcystis Blooms

ABSTRACT Blooms of the toxin-producing cyanobacterium Microcystis are increasing globally, leading to the loss of ecosystem services, threats to human health, as well as the deaths of pets and husbandry animals. While nutrient availability is a well-known driver of algal biomass, the factors controlling “who” is present in fresh waters are more complicated. Microcystis possesses multiple strategies to adapt to temperature, light, changes in nutrient chemistry, herbivory, and parasitism that provide a selective advantage over its competitors. Moreover, its ability to alter ecosystem pH provides it a further advantage that helps exclude many of its planktonic competitors. While decades of nutrient monitoring have provided us with the tools to predict the accumulation of phytoplankton biomass, here, we point to factors on the horizon that may inform us why Microcystis is presently the dominant bloom former in freshwaters around the world.