Browsing by Subject "Nutrient enrichment"

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  • Angove, Charlotte; Norkko, Alf; Gustafsson, Camilla (2018)
    Aquatic plant meadows are valuable components to the 'coastal filter' and it is important to understand the processes that drive their ability to cycle nutrients. However, at present, the field-based evidence for understanding the drivers of nutrient uptake by plants is lacking. This study aimed to investigate how well individual shoots of aquatic plants could meet their nitrogen demands using the sediment nutrient pool (porewater ammonium) and to explore which traits helped to facilitate such uptake. Several species were investigated in shallow, submerged (2-4 m) mixed-species communities in the northern Baltic Sea using incubation experiments with enriched ammonium. After a 3.5 h incubation time, individuals were collected and analysed for nitrogen (% DW) and N-15 (at-%) concentrations. Uptake by plants was calculated per unit nitrogen in response to the N-15 labelled source and to overall nitrogen availability. Background porewater ammonium availability was highly variable between individual plants. Species identity did not significantly affect uptake metrics and the effect of ambient porewater availability was weak. As biomass increased there were significant logarithmic declines in the 95th quantiles of nutrient uptake rates, ambient porewater nutrient availability and aboveground nitrogen tissue concentrations (% DW). Such findings suggested that uptake rates of plants were significantly demand driven and the nutrient conditions of the porewater were significantly driven by the demands of the plant. Findings parameterised the unfulfilled potential for some aquatic plants to cycle nutrients more efficiently and highlighted the potential importance of access to new nutrient sources as a way of enhancing nutrient cycling by aquatic plants. Plant traits and community properties such as the activity of infauna could facilitate such an access and are likely important for nutrient uptake.
  • Roth, Florian; El-Khaled, Yusuf C.; Karcher, Denis B.; Rädecker, Nils; Carvalho, Susana; Duarte, Carlos M.; Silva, Luis; Calleja, Maria Ll.; Moran, Xose Anxelu G.; Jones, Burton H.; Voolstra, Christian R.; Wild, Christian (2021)
    Ecosystem services provided by coral reefs may be susceptible to the combined effects of benthic species shifts and anthropogenic nutrient pollution, but related field studies are scarce. We thus investigated in situ how dissolved inorganic nutrient enrichment, maintained for two months, affected community-wide biogeochemical functions of intact coral- and degraded algae-dominated reef patches in the central Red Sea. Results from benthic chamber incubations revealed 87% increased gross productivity and a shift from net calcification to dissolution in algae-dominated communities after nutrient enrichment, but the same processes were unaffected by nutrients in neighboring coral communities. Both community types changed from net dissolved organic nitrogen sinks to sources, but the increase in net release was 56% higher in algae-dominated communities. Nutrient pollution may, thus, amplify the effects of community shifts on key ecosystem services of coral reefs, possibly leading to a loss of structurally complex habitats with carbonate dissolution and altered nutrient recycling.
  • Luoto, Tomi P.; Rantala, Marttiina V.; Tammelin, Mira H. (2017)
    We examined a sediment record from Lake Hiidenvesi in southern Finland using paleolimnological methods to trace its limnoecological history. In our record, beginning from the 1940s, chironomid (Diptera) assemblages shifted from typical boreal taxa towards mesotrophic community assemblages at similar to 1960-1980 CE being finally replaced by eutrophic taxa from the 1990s onward. The diatom (Bacillariophyceae) assemblages reflected relatively nutrient rich conditions throughout the record showing a further increase in eutrophic taxa from the 1970s onward. A chironomid-based reconstruction of late-winter hypolimnetic dissolved oxygen (DO) conditions suggested anoxic conditions already in the 1950s, probably reflecting increased inlake production due to allochthonous nutrient inputs and related increase in biological oxygen consumption. However, the reconstruction also indicated large variability in long-term oxygen conditions that appear typical for the basin. With regard to nutrient status, chironomid- and diatom-based reconstructions of total phosphorus (TP) showed a similar trend throughout the record, although, chironomids indicated a more straightforward eutrophication process in the benthic habitat and seemed to reflect the intensified human activities in the catchment more strongly than diatoms. The DO and TP reconstructions were mostly similar in trends compared to the measured data available since the 1970s/1980s. However, the increase in TP during the most recent years in both reconstructions was not visible in the monitored data. The results of our multiproxy study emphasize the significance of including both epilimnetic and hypolimnetic systems in water quality assessments and provide important long-term limnoecological information that will be useful in the future when setting targets for restoration.