Mollusc communities of lowland rivers and oxbow lakes in agricultural areas with anthropogenically elevated nutrient concentration

Abstract

Anthropogenically elevated nutrient concentration occurs in both ground and surface waters and cause grave environmental problems which are responsible for the degradation of water quality on a worldwide scale. The progressive anthropogenic pressure caused by prolonged agricultural activity has a negative effect on most water ecosystems including rivers and reservoirs. Freshwater molluscs, which are hololimnic organisms, have a limited mobility; therefore, they are good bioindicators of changes in their habitats. They reflect the abiotic or biotic state of water habitats, which represents the impact of environmental change on the habitat, community as well as on the ecosystem. A long-term survey of mollusc communities revealed the occurrence of 44 species including some rare, vulnerable, threatened or legally protected species, e.g. Borysthenia naticina, Unio crassus, Anodonta cygnea, Pseudanodonta complanata or Sphaerium rivicola, in the Wkra River, its tributaries and selected oxbow lakes. In the Wkra River catchment area, the mollusc communities, including U. crassus (Habitats Directive Natura 2000), are under a combined effect of several environmental factors. Conductivity, hardness, current velocity, river width, temperature, nutrient concentration and the size of sediment particles were the parameters most associated (statistically significant according to the forward selection results) with the distribution of mollusc species. The forward selection results showed that the concentration of dissolved oxygen and the occurrence of macrophytes also exerted a significant influence on the distribution of Mollusca. Among environmental factors, anthropogenically elevated concentrations of nitrites and nitrates in the water were the most predictive parameters that negatively influenced (stressors) the structure of mollusc communities. The novel findings of this survey showed that some mollusc species could tolerate wider ranges of some environmental factors and higher concentrations of nutrients than had been expected. U. crassus is more tolerant of a relatively high concentration of nitrates in the water than was previously expected, as well as of nitrites and phosphates, and it can survive in rivers with relatively high nutrient concentration. The present results confirm both the field and the toxicological research on the negative effect of nitrites and nitrates, which is caused by their toxicity to freshwater molluscs. The number of individuals, number of mollusc species and density decreased dramatically within the last year of the survey in the Wkra River and its tributaries. This phenomenon seems to be a direct result of the nutrient enrichment in the Wkra River catchment area, the regulation of riverbeds or an indirect result, e.g. lack of primary or appropriate host fishes for unionid species. The declining trend in the global mollusc population has probably begun to occur in the Wkra River catchment area.

The influence of the landscape structure within buffer zones, catchment land use and instream environmental variables on mollusc communities in a medium‐sized lowland river

“…3 of bacteria and fungi, which also constitute food resources for molluscs, increases with the nutrients that flow off agricultural lands. Therefore, an increase in mollusc growth, fecundity and population abundance can be observed, but only up to the threshold value of the nutrient concentration in the water (Lewin 2014;Strayer 2014). Our results also confirmed and supported those obtained by Theodoropoulos et al (2015), who found that agriculture and development were positively correlated with the distribution of molluscs, including Lymnaeidae and Planorbidae.…”

“…Among these, two endangered bivalve species, the thick-shelled river mussel U. crassus and the swan mussel A. cygnea, are regarded as Vulnerable (VU) and Near Threatened (NT), respectively, in Europe according to the European Red List of Non-marine Molluscs (Cuttelod et al 2011). The main reasons for the threat are changes in the physical and chemical parameters of the water, eutrophication (especially elevated concentration of nitrates in running waters), the regulation of rivers, the exploitation of sand and gravel from the river corridors, dredging and weed cutting as well as habitat modification and destruction (Aldridge 2000;Bogan 2008;Lewin 2014). Freshwater mussels (Unionoidea) are one of the most imperilled faunal groups on a global scale.…”

Long-term changes in the malacofauna of the pond-type experimental lake Warniak (Mazurian Lakeland, North-Eastern Poland)

“…The density of Unionidae in lake Warniak, especially that of A. cygnea, was comparable to the values reported from some oxbow lakes of the Bug, Pilica and Wkra rivers (aBraszEwska-kowaLczyk 2002, LEwandowski 2006, LEwin 2014. The proportion of unionids in the abundance of mollusc assemblages in Warniak was high (14.4% and 27.2% in 1998 and 2015, respectively).…”

“…loDge 1985, PiP 1987, hanson 1990, costiL & cLEmEnt 1996, mouthon 1996, BatzEr et al 2000, JurkiEwicz-karnkowska 2011, LEwin 2014, seem to limit the mollusc species richness and abundance in Warniak. The trophic state has not changed significantly during the 17 years, whereas the macrophytes were considerably sparser in 2015 than in 1998.…”

Fishes in Paleochannels of the Lower Mississippi River Alluvial Valley: A National Treasure

“…Though these species have large body sizes, as physostomous, they are able to gulp air from the atmosphere if dissolved oxygen is low enough to prevent efficient oxygen transfer through gills (Smatresk and Cameron 1982). Freshwater Drum are also tolerant of high temperature, low dissolved oxygen, turbidity, and eutrophic conditions (Meador and Carlisle 2007) and may be attracted to paleochannels by high availability of macroinvertebrates in sediment (Cochran and Harp 1990;Lewin 2014).…”