Seasonally variable riverine production in the Venezuelan llanos

Abstract

We examined primary production, respiration, and nutrient dynamics in littoral areas of the mainstem and lagoons of the Cinaruco, a nutrient-poor river in the Venezuelan llanos. Gross primary productivity (GPP) was relatively high, given the poor nutrient conditions in this river. Seasonal variability in net ecosystem production (NEP) was also high, with highest values occurring in the dry season (March-April) when fish biomass and chlorophyll a (both water-column and benthic) levels were greatest (dryseason NEP ¼ 542 mg C m À2 d À1 , wet-season NEP ¼ 303 mg C m À2 d À1 ). NEP and algal biomass (measured as chlorophyll a) were higher in lagoons than at river sites, with more pronounced differences between these 2 habitats during the dry season. Strong N limitation was evident. Dissolved inorganic N (DIN) concentrations always were ,2 lM and typically were ,0.5 lM. Molar ratios of DIN:SRP (soluble reactive P) varied little seasonally and were always ,8. As in other Neotropical aquatic systems, water-column productivity was an important source of organic matter and was .23 benthic productivity, even in shallow regions of the riverine ecosystem. Low nutrient levels combined with high rates of autochthonous productivity in the littoral zone of this river suggest extremely rapid nutrient cycling rates and support the view that the littoral regions may be important in providing the organic matter that maintains secondary production, consistent with the Riverine Productivity Model and other observations in the Orinoco Basin.

Carbon sink to source: longitudinal gradients of planktonic P:R ratios in subtropical reservoirs

“…In contrast, volumetric respiration, although influenced by nutrient enrichment, was not significantly correlated to location in these reservoirs. In addition, our comparatively high productivity rates and corresponding autotrophic conditions measured in inflow zones are consistent with results reported by Cotner et al (2006) who found autotrophy in tropical riverine zones typified by warm, shallow waters. These riverine contributions of autochthonous production can yield labile C sources important to respiration and secondary production at downgradient open-water zones.…”

Longitudinal trends and discontinuities in nutrients, chlorophyll, and suspended solids in the Upper Mississippi River: implications for transport, processing, and export by large rivers

“…Thus, light availability and residence time were both plausible mechanisms for the observed lower concentrations of CHL in the OR reach. In addition, backwaters and side arms of rivers often have higher phytoplankton standing stock than the main channel (Baker & Baker, 1979;Cotner et al, 2006) and backwaters contiguous with the main channel may be sources of phytoplankton in some rivers (e.g., Ahearn et al, 2006). The lack of contiguous backwater areas in the OR reach may also have contributed to its lower CHL.…”

Aquatic metabolism short-term response to the flood pulse in a Mediterranean floodplain

“…However, despite the key effect of hydrological linkages on the structure and function of floodplain ecosystems, there are few studies tracking short-term changes in water chemistry during floods, and their effects on aquatic metabolism, across the different habitats present in the floodplain. Moreover, most of the information focuses on a few rivers such as the temperate Rhine and Danube rivers (Vandenbrink et al, 1993;Heiler et al, 1995;Tockner et al, 1999;Hein et al, 2004), and the tropical Paraguay, Amazon and Orinoco rivers (Hamilton & Lewis, 1987;Forsberg et al, 1988;Hamilton et al, 1995;Castillo, 2000;Cotner et al, 2006). Unlike tropical and temperate systems, Mediterranean floodplains are marked by highly variable discharges with unpredictable floods and severe droughts, which affects the structure and function of the whole riverfloodplain ecosystem (Gasith & Resh, 1999;Bonada et al, 2007).…”