Floodplain rehabilitation and the importance of nitrogen dynamics for plant communities

This thesis addressed the question whether changes in river water quality and sediment characteristics due to human impact, in combination with strongly altered flooding regimes, would form a constraint for the ecological development of floodplain habitats with species-rich vegetation types. Besides floodplain restoration activities in the lower reaches of rivers, the project also aimed at investigating opportunities for restoration of estuaries. Several extensive field surveys in highly impacted, rehabilitated and also more natural floodplains of non-tidal rivers (the Netherlands and Poland) and in estuarine floodplain locations (the Netherlands and Ireland) were carried out to investigate correlations between vegetation parameters and nutrient-related sediment and water characteristics. In large-scale mesocosm experiments, highly frequent, detailed measurements of environmental parameters, plant variables as well as process rates in soil-vegetation monoliths were carried out. The focus was on the effects of flooding during the growing season and renewed influence of tide and brackish water. The field studies in the non-tidal river floodplains revealed that there were strong positive correlations of peak standing crop to the soil nitrogen content for the pristine river floodplains, indicating that plant growth is limited by nitrogen, which was confirmed by our analysis of tissue nutrient ratios in aboveground living biomass. These correlations were absent for regulated, impacted river systems, suggesting that primary productivity is no longer controlled by nitrogen there. Under experimental conditions it turned out that in soil monoliths of these heavily regulated systems vegetation was much less adapted to a flooding event during the growing season compared to communities from more natural sites. A similar effect of eutrophication on plant growth limitation and productivity was expected for estuarine floodplains. Instead, tidal amplitude in relation to an elevation gradient, rather than nutrient richness, turned out to be determining the distribution and productivity of the dominant helophyte plant species in the brackish zone of these estuaries. In experimental conditions the tidal movement increased nitrogen transformation rates in former estuarine sediments with and without agricultural use. Mineralization was enhanced by tidal water level fluctuations, resulting in higher inorganic nitrogen availability. In contrast to expectations, brackish treatments had no negative effects on plant biomass production in the agricultural grassland soils, while it did have a negative effect on productivity of the vegetation from the former brackish marsh. The different responses of the floodplain types investigated are directly relevant in discussions on rehabilitation strategies for modified non-tidal river floodplain systems. Measures promoting summer flooding should be considered with care, as it might lead to enhanced nutrient availability in the soil and is potentially detrimental for the plant communities present in the area. In estuarine systems, the emphasis of restoration practices should be on re-establishing a tidal gradient with sufficient amplitude as this is more important for species distribution compared to a salinity gradient, additionally reducing available nutrient concentrations is of much less importance as plant growth is not limited by nutrient availability in the soil

Moerasbufferstroken langs watergangen: haalbaarheid en functionaliteit in Nederland

Internationale regelgeving, zoals de Kaderrichtlijn Water en de nitraatrichtlijn, versterkt de aandacht voor bufferstroken, bemestingsvrije zones, helofytenfilters en natuurvriendelijke oevers als voorzieningen voor de reductie van de emissie van nutriënten en voor de vergroting van natuurwaarden. In dit rapport ligt de focus op natte bufferzones (moerasbufferstroken) langs landbouwpercelen. In tegenstelling tot droge bufferstroken heeft dit type bufferstroken een grote potentie voor het waterbeheer. In combinatie met drainagesystemen leveren ze mogelijk een relevante bijdrage in de zuivering van nutriëntenrijk grondwater. Daarmee is het aanleggen van dit soort voorzieningen een mogelijke maatregel in het kader van het stroomgebiedsbeheer (KRW). Om de claims van effectiviteit te onderzoeken is twee jaar lang onderzoek gedaan naar het functioneren van moerasbufferstroken. Dit onderzoek is gecombineerd met een kosten- baten analyse

Moerasbufferstroken: potenties voor nutriëntenverwijdering en economisch rendement - een case study in westelijk Noord-Brabant

Diffuse belasting van het oppervlaktewater met nutriënten vormt een probleem voor het waterbeheer in Nederland. De inzet van ecotechnologische maatregelen kan bijdragen aan de reductie van de emissies. Met name moerasbufferstroken, waarbij het te zuiveren water in contact komt met de bovenste bodemlagen, laten een hoge verwijdering zien. In dit artikel staat een onderzoek centraal naar de werking van een moerasbufferstrook langs de Strijbeekse beek (Noord-Brabant), waarbij het drainagewater direct in de bufferstrook uitkomt, én het economische rendement van zo’n systeem. De verwijdering van stikstof blijkt beperkt door de hoge kweldruk en daaruitvolgende lage infiltratie van drainagewater. De verwijdering van fosfaten is juist hoog vanwege de hoge adsorptiecapaciteit van de bodem door de aanwezigheid van ijzerionen. Met een alternatieve inrichting en beheer is het mogelijk ook de verwijderingsefficiëntie voor stikstof te verhogen. Uit de economische analyse komt naar voren dat de bufferstrook van 350 meter niet rendeert. Indien bufferstroken met een gezamenlijke lengte van 6,5 kilometer zouden worden aangelegd, zijn meer maatschappelijke baten te verwachten, maar dan nog zijn deze niet voldoende om op te wegen tegen de kosten van uit productie genomen landbouwgron

Response of the sulfate-reducing community to the re-establishment of estuarine conditions in two contrasting soils: a mesocosm approach

We studied the response of the sulfate-reducing prokaryote (SRP) communities to the experimental variation of salinity and tide in an outdoor mesocosm setup. Intact soil monoliths were collected at two areas of the Haringvliet lagoon (The Netherlands): one sampling location consisted of agricultural grassland, drained and fertilized for at least the last century; the other of a freshwater marshland with more recent sea influence. Two factors, i.e., “salinity” (freshwater/oligohaline) and “tide” (nontidal/tidal), were tested in a full-factorial design. Soil samples were collected after 5 months (June–October). Dissimilatory (bi)sulfite reductase β subunit-based denaturing gradient gel electrophoresis (dsrB-DGGE) analysis revealed that the SRP community composition in the agricultural grassland and in the freshwater marshland was represented mainly by microorganisms related to the Desulfobulbaceae and the Desulfobacteraceae, respectively. Desulfovibrio-related dsrB were detected only in the tidal treatments; Desulfomonile-related dsrB occurrence was related to the presence of oligohaline conditions. Treatments did have an effect on the overall SRP community composition of both soils, but not on the sulfate depletion rates in sulfate-amended anoxic slurry incubations. However, initiation of sulfate reduction upon sulfate addition was clearly different between the two soils.

Biogeochemical constraints on the ecological rehabilitation of wetland vegetation in river floodplains

The European policy for river management during peak discharge periods is currently changing from exclusion strategies (reinforcement of dykes) to allowing a more natural situation by creating more floodplain space to reduce water levels during peak discharges. In addition, water retention and water storage areas have been created. The new measures are generally being combined with nature development strategies. Up till now, however, ecological targets of broadscale floodplain wetland restoration including sedge marshes, species-rich floodplain forests and carrs, riparian mesotrophic grasslands and other biodiverse riverine ecosystems, have hardly developed in these areas. Most studies on the conditions needed for sustainable ecological development of floodplains have focused on hydrological and geomorphological rather than biogeochemical issues (including nutrient availability and limitation). There are, however, large differences in the composition of river water and groundwater and in sediment quality between rivers in densely populated areas and those in more pristine areas, which serve as a reference. It is very likely that these factors, in combination with heavily altered hydrological regimes and the narrow areas confined between the dykes on both sides of the rivers, impose major constraints on sustainable ecological development of riverine areas. Another issue is that existing wetlands are generally considered to be very appropriate for water retention and conservation, although recent research has shown that this may pose a serious threat to their biodiversity. The present paper reviews the biogeochemical constraints on the combination of floodplain rehabilitation, water conservation and the conservation and development of wetlands. It is concluded that biogeochemical problems (mainly related to eutrophication) predominantly arise in less dynamic parts of the river system, to which the flood-pulse concept applies less. Sound knowledge of the biogeochemical processes involved will contribute to greater efficiency and a better prediction of the opportunities for restoration and development of riverine wetlands. This information can be directly applied in nature management, water management, policy-making and consultancy. [KEYWORDS: biodiversity ; biogeochemistry ; eutrophication ; flooding ; nature conservation ; review ; water management]

Effects of increased salinity and tide in the Haringvliet on biogeochemical processes; a mesocosm experiment

Item does not contain fulltextSymposium Soil & Water 200

The decline of metallophyte vegetation in floodplain grasslands: Implications for conservation and restoration

Contains fulltext : 75702.pdf (publisher's version ) (Closed access)12 p