Lake eutrophication and its ecosystem response

Abstract

China is a country with many lakes, about one-third of which are freshwater mainly distributed in the middle and lower reaches of the Yangtze River. Currently most of the lakes are mesotrophic or eutrophic. Lake eutrophication has become one of the major ecological and environmental problems faced by lakes in China and can lead to a series of abnormal ecosystem responses, including extinction of submerged plants, frequent occurrence of cyanobacterial blooms, increased microbial biomass and productivity, decreased biodiversity, accelerated cycles, and a change in the efficient use of nutrients. With development of eutrophication, the whole lake ecosystem suffers decreased biodiversity, simplification of biotic community structure, instability of the ecosystem, and ultimately the clear-water, macrophyte-dominated ecosystem gradually shifts to a turbid-water, algae-dominated ecosystem. This ecosystem succession mechanism is speculated to be caused by different nutrient utilization efficiencies of macrophytes and phytoplankton. The ultimate ecosystem succession trend of seriously eutrophic lakes is that a phytoplankton-dominated autotrophic lake shifts to a heterotrophic lake dominated by micro-organisms, protozoans. Today, eutrophication generally refers to trophic state arising from increased nitrogen and phosphorus input, specifically, increased discharge of plant nutrients (mainly nitrogen and phosphorus) from industrialization, agricultural modernization, and urbanization.Nitrogen, phosphorus, and some other elements are essential for plant growth; however, if a water body receives more nitrogen and phosphorus than necessary, the ecosystem can experience changes such as algal blooms; therefore, eutrophication can be considered as a biological or ecological concept. In this sense, using nitrogen, phosphorus, or other environmental factors is not the most appropriate way to evaluate the trophic level of a lake or reservoir; instead, the evaluation should be based on primary productivity of macrophytes and phytoplankton, but these indicators are difficult to assess. Alternatively, nitrogen, phosphorus, transparency, and chlorophyll a are commonly used as indicators for evaluation of eutrophication.OECD proposed the following thresholds of eutrophication in 1982: average total phosphorus concentration >0.035 mg/L; average chlorophyll a concentration >0.008 mg/L; and average transparency <3 m [2]. According to these thresholds, many lakes in China have become eutrophic. An assessment of the trophic status of lakes in the middle and

Responses of chlorophyll and MDA ofVallisneria natansto nitrogen and phosphorus availability and epiphytic algae

“…During the growing season, TN and TP concentrations were low (<4.5 and <0.45 mg P/L) in natural eutrophic lakes in China (Qin et al 2013). According to the results of this experiment and recent research about relationships between nutrients and planktonic algae in eutrophic lakes Sheng et al 2012), water column nutrient loading should not directly cause stress to submerged plants.…”

“…T: epiphytic algae from submerged plants in Lake Taihu; T1, T2, T3, and T4 as in Figure 1. (<4.5 and <0.45 mg/L, respectively; Qin et al 2013). Thus, water column nutrient loading might benefit the growth of V. nanas when considering N and P concentrations only.…”

“…However declines of submerged macrophytes have been observed in many eutrophic lakes throughout the world (Hough et al 1989;Touchette & Burkholder 2000;Ansari et al 2011) and the declines are often associated with anthropogenic nutrient loading (Duarte 2002;Hauxwell et al 2003;Orth et al 2006;Waycott et al 2009;Ruhl & Rybicki 2010;Xu et al 2010). At present, the problem of lake eutrophication is still serious (Qin et al 2013). The disappearance of submerged macrophytes and the switch to a turbid phytoplankton-dominated state is still one of the most serious problems caused by eutrophication in shallow lakes (Hilt et al 2006;Qin et al 2013), while the mechanisms that lead to the loss of submerged macrophytes at high N and P concentrations are not well understood.…”

“…At present, the problem of lake eutrophication is still serious (Qin et al 2013). The disappearance of submerged macrophytes and the switch to a turbid phytoplankton-dominated state is still one of the most serious problems caused by eutrophication in shallow lakes (Hilt et al 2006;Qin et al 2013), while the mechanisms that lead to the loss of submerged macrophytes at high N and P concentrations are not well understood. Some researchers hold that high N and P concentrations have a directly adverse effect on submerged macrophytes (Burkholder et al 1992;Chen et al 2002;Cao et al 2004, Nimptsch & Pflugmacher 2007.…”

Factors influencing tropical Island freshwater fishes: species, status, threats and conservation in Hainan Island

“…In the past twenty years, water pollution has increased rapidly in China, along with rapid economic development (Qin et al, 2013). Now, many rivers and reservoirs have been polluted by agriculture, industry, and rapid urbanization in Hainan Island (Zhao, 2015).…”