Patricia Rodríguez

Terrestrial organic matter input suppresses biomass production in lake ecosystems

Terrestrial ecosystems export large amounts of organic carbon (t-OC) but the net effect of this OC on the productivity of recipient aquatic ecosystems is largely unknown. In this study of boreal lakes, we show that the relative contribution of t-OC to individual top consumer (fish) biomass production, and to most of their potential prey organisms, increased with the concentration of dissolved organic carbon (DOC; dominated by t-OC sources) in water. However, the biomass and production of top consumers decreased with increasing concentration of DOC, despite their substantial use (up to 60%) of t-OC. Thus, the results suggest that although t-OC supports individual consumer growth in lakes to a large extent, t-OC input suppresses rather than subsidizes population biomass production.

Benthic organic carbon release stimulates bacterioplankton production in a clear-water subarctic lake

Abstract. We carried out a set of experiments in a small clear-water lake in northern Sweden during summer 2010 to assess the effect of organic C (OC) released from epipelic algae on pelagic bacterial production (BP). The release rate of OC (dissolved and particulate) from epipelic algae was ∼45.4 ng C m−2 h−1. Bacterioplankton uptake of dissolved OC was P-limited, and pelagic primary production (PP) was colimited by N and P. Pelagic BP (3.2 ± 6 µg C L−1 h−1) exceeded pelagic PP (0.012 ± 0.008 µg C L−1 h−1). Pelagic BP was higher in lake water in contact with sediments and the epipelic algae growing on their surface than in water separated from the sediments. Epipelic algae release OC to lake water and potentially stimulate pelagic BP. However, exploitation of benthic OC probably is suboptimal because of nutrient limitation (primarily by inorganic P) of BP.

The sudestadas : a hydro-meteorological phenomenon that affects river pollution (River Luján, South America)

Abstract The “sudestadas” are short-term hydro-meteorological phenomena that produce a “hydraulic plug”, preventing the normal drainage of the water courses in the Río de la Plata Estuary. The purpose of this study was to analyse the influence of the sudestadas on the water quality of the Lower River Luján, which discharges into the Río de la Plata Estuary (59°37′W; 34°43′S). Samplings were conducted from November 1998 to July 2001 at six sites on the lower stretch of river. Physical and chemical variables were measured and a nonparametric test was applied to each variable, grouping samples affected and non-affected by sudestadas, which further diminish the water quality of the river. The frequency and intensity of sudestadas are predicted to increase as a consequence of the Earths warming; thus, this research suggests that the environmental risk produced by the effects of global change, will be greater.

Effects of Terrestrial Organic Matter on Aquatic Primary Production as Mediated by Pelagic-Benthic Resource Fluxes

Flows of energy and matter across habitat boundaries can be major determinants of the functioning of recipient ecosystems. It is currently debated whether terrestrial dissolved organic matter (tDOM) is a resource subsidy or a resource subtraction in recipient lakes. We present data from a long-term field experiment in which pelagic phosphorus concentration and whole-ecosystem primary production increased with increasing tDOM input, suggesting that tDOM acted primarily as a direct nutrient subsidy. Piecewise structural equation modeling supports, however, a substantial contribution of a second mechanism: colored tDOM acted also as a resource subtraction by shading benthic algae, preventing them from intercepting nutrients released across the sediment–water interface. Inhibition of benthic algae by colored tDOM thus indirectly promoted pelagic algae and whole-ecosystem primary production. We conclude that cross-ecosystem terrestrial DOM inputs can modify light and nutrient flows between aquatic habitats and alter the relative contributions of benthic and pelagic habitats to total primary production. These results are particularly relevant for shallow northern lakes, which are projected to receive increased tDOM runoff.

Phytoplankton and Periphyton Primary Production in Clear and Turbid Shallow Lakes: Influence of the Light Environment on the Interactions between these Communities

The ecological relevance of shallow lakes has been largely documented. The Pampean plain (Argentina) holds one of the main wetlands of South America, constituted by thousands of shallow lakes which provide valuable ecosystem services, and can be found in any of three regimes: clear-vegetated, inorganic-turbid or phytoplankton-turbid. Since these lakes play an important role in the global carbon balance, metabolism studies encompassing phytoplankton and periphyton under different regimes become relevant. Here, we analyzed the primary production (PP) of phytoplankton and periphyton in three Pampean shallow lakes representing the main types mentioned. The relative contribution of each algal community to the joint PP was different in each lake and related to their regime. The periphyton contribution was higher in the clear-vegetated lake than in the turbid lakes. The phytoplankton-turbid lake exhibited the highest PP for both communities. The inorganic-turbid lake presented the highest light limitation; nonetheless, the efficiency of periphyton in this lake showed an increasing trend with depth, suggesting light acclimation. Although phytoplankton dominated the PP in the three lakes, periphyton contribution was also important, particularly in the clear-vegetated lake. Our results emphasize that the PP of attached communities should be considered to estimate the PP of the whole lake.