Fluxes of carbon and nutrients through the inflows and outflow of Lake Võrtsjärv, Estonia

Abstract

We determined the incoming fluxes of total organic carbon (TOC), dissolved inorganic (DIC) and organic carbon (DOC), nitrogen, phosphorus, and silicon via four main inflows into Lake Võrtsjärv and compared these with the outgoing fluxes from the lake during 2008-2009. The discharge and loads of the studied substances from the four main rivers alone were higher than the amounts carried out of the lake in 2008. In 2009, the outflow of water exceeded the inflows and this was the case with the amounts of TOC, DIC, and DOC as well. However, the incoming load of nutrients was continuously higher than the outgoing load. The lake accumulated nutrients (nitrogen, phosphorus, and silicon) irrespective of whether water retention was positive or negative, but the balance between carbon accumulation and carbon emission depended on the lake's water budget.

Contributions of autochthonous and allochthonous sources to dissolved organic matter in a large, shallow, eutrophic lake with a highly calcareous catchment

“…It also reflects changes in DOM due to photochemical and microbial processes and to sedimentation. These results confirm that Võ rtsjä rv is an active site for transport, transformation, and storage of considerable amounts of carbon received from the catchment area (Pall et al 2011;F. Cremona unpubl.…”

“…The main objectives of our study were to assess the origin of DOM and estimate the proportion of Al-DOM and Au-DOM in a large shallow eutrophic lake by using d 13 C analyses and complementary methods. Based on the highly eutrophic status of Lake Võ rtsjä rv and on the fact that it receives about three times more DIC than DOC from its highly calcareous catchment (Pall et al 2011), a rather high proportion of Au-DOM might be expected. However, considering that the lake is very shallow and its volume compared to the catchment area is rather small, we still hypothesized a rather large proportional contribution of Al-DOM, with strong spatial and temporal variation due to the seasonality of riverine inflows, phytoplankton development and meteorological conditions.…”

Characteristics of dissolved organic matter in the inflows and in the outflow of Lake Võrtsjärv, Estonia

“…The discharge of the inflows is the highest during the snow melting in spring and in the rainy autumn period. Low discharge appears in summer and in winter (Pall et al, 2011).…”

“…In Estonia the concentration of DOC in some rivers was recently studied by Pall et al (2011) and its spectroscopic properties were assessed by Selberg et al (2011). The present study addresses the impact of catchment land use on DOM concentration in rivers.…”

Spatial and annual variability of environmental and phytoplankton indicators in Lake Võrtsjärv: implications for water quality monitoring

“…Discharge of total nitrogen (TN) and phosphorus (TP) to the lake has decreased since 1980 (Järvet, 2004;Pall et al, 2011). Monitoring data show a clear increasing trend in permanganate oxygen demand in the lake whereas TN and TP concentrations have decreased since the 1980s, especially in summer and autumn, reaching annual mean values of 1.38 mg L -1 for TN and 47.8 µg L -1 for TP in the period 1994-2010.…”