Organic Sediment Nutrient Concentrations and their Relationship with the Hydrological Connectivity of Floodplain Waters (River Havel, NE Germany)

Abstract

Investigations on large canalised rivers, for example the Danube, have shown that transported particulate matter, which is typically inorganic, is predominantly deposited in waters near the river's main channel. This investigation deals with the lower section of the River Havel (NE Germany), a canalised lowland river with a very flat floodplain. This river is highly polluted by nutrients from urban areas (Berlin) and a long chain of river lakes produces high concentrations of phytoplankton. Due to the high proportion of planktogenic detritus, it was hypothesised that greater quantities of nutrient-rich fine particulate organic matter (FPOM) would be deposited in floodplain waters located further from the main channel than has been reported for large rivers. The total nutrient, P-binding metal (Fe, Al, and Mn), organic and inorganic carbon (TOC, TIC) contents of the upper organic sediment layer (0-4 cm) were analysed in samples collected from 48 floodplain water and river sites. The sediment bulk density, calculated on the basis of dry mass content and loss on ignition, was used to characterise the waters according to the impact of the river current. The results showed that the variability of total phosphorus (TP) was best explained by the variability of total iron (TFe, R 2 = 0.52). The floodplain water sediments could clearly be separated into two groups on the basis of the sediment particle size composition, and of the element ratios TOC:TP, TN:TP, primarily TFe:TP. The sediments from impounded river sections and from mouth sections of backwaters (approx. 100-200 m) were characterised by a high proportion particles from the 0.1 to 0.5 mm size fraction and by homogeneous, low TFe:TP, TOC:TP and TN:TP ratios. Sediments from distal sections of backwaters and of oxbow lakes tended to exhibit high element ratios with much higher variability. These results were interpreted as a spatially limited impact of the river on the floodplain water sediments. Contrary to expectation, the phosphorus bound in river seston was predominantly and very homogeneously deposited in the impounded river and mouth sections of backwaters. This implies that the inundation of the floodplain waters during spring floods seems to have no important material impact on the sediments in waters of low hydrological connectivity with the River Havel.

Effects of Oxbow Reconnection Based on the Distribution and Structure of Benthic Macroinvertebrates

“…The bottom of the river was composed of fine sand. The shallow water benthos samples were collected with an 80-cm 2 Wolnomiejski grab and from the central deeper water with a 225-cm 2 Ekman-Birge grab. Four grabs were collected for each sample at each site.…”

“…These differences refer to attribute such as the stage of ecological succession. Authors (e.g., [1][2][3]) point to the importance of hydrological connectivity between the river channel and an oxbow lake, as a key process in water-mediated transfer of energy, sediment, organic matter, and organisms.…”

Spatial variability in floodplain sedimentation: the use of generalized linear mixed-effects models

“…Focussing on organic carbon (TOC) and nitrogen (TN), deposition during overbank floods is an important ecosystem function which provides important benefits as water quality enhancement or mitigation of greenhouse effect (Johnston, 1991;Day et al, 2004;Verhoeven et al, 2006, IPCC, 2007. At the reach scale, TOC and TN exchange between the main channel and its adjacent floodplain plays a key role in the ecological functioning (Junk, 1999;Robertson et al, 1999;Tockner et al, 1999;Tockner at al., 2000;Thoms, 2003;Knosche, 2006;Preiner et al, 2008). Previous research has shown how human-induced changes at the basin and reach scale have decreased the potential of riverine floodplains to act as sediment-associated nutrient sinks (Noe and Hupp, 2005;Owens et al, 2005;Pierce and King, 2008;Cabezas et al, 2009;Cabezas and Comin, 2010).…”

Short-term effects of drawing water for connectivity of rivers and lakes on zooplankton community structure

“…The reason for the differences at site 3 may result from great amount of nutrition and plankton and landscape geometry from narrow stream channel (at site 2) to wide lake body with slower velocity of water flow (at site 3). Knösche (2006) found that the sediments from impounded river sections and from mouth sections of backwaters were characterised by a high proportion of particles from 0.1 to 0.5 mm size fractions, and sediments from distal sections of backwaters and of oxbow lakes tended to exhibit high element ratios with much higher variability, so these results were interpreted as a spatially limited impact of the river on the floodplain water sediments.…”

“…Connectivity of lakes and rivers, especially some urban lakes, were separated from each other because of the reconstructive activities of human such as enclosing lakes for aquaculture or impoldering lakes for building (Aoyagui and Bonecker, 2004;Cottenie and De Meester, 2003;Knösche, 2006). These obstructed lakes were usually eutrophicated for the input of sewage water, industrial wastewater or aquaculture water (Daniel et al, 1998;Correll, 1998).…”