Homogenisation of ECosystem functioning between Temperate and Neotropical streams due to AgRicultural land usE (HECTARE)
Final Report Abstract
The conversion of natural into agricultural landscapes represents a pervasive alteration of the environment and has been identified as the most important driver of the loss of global biodiversity. The intensity at which natural are converted into agricultural areas has decreased during the last three decades but the existing arable land is subjected to agricultural intensification. The simultaneous alteration of physical, chemical and habitat properties of running waters following agriculture may affect all levels of biological organisation and can be expected to translate into persistent adverse effects on ecosystem functioning. The project HECTARE was designed as a whole-ecosystem approach combined with a food web perspective and represented a novel research approach for understanding of the effects of agricultural land use on the functioning of lotic ecosystems. The comparison the response of functions and structure showed that contemporary agricultural land use has substantial direct and indirect effect that go beyond of those described in previous studies. Among the studied ecosystem functions, nutrient cycling and primary production were most impacted and agricultural streams had significantly lower retention of t-DOC and t-TDN. This indicates that by converting forested into agricultural streams, we are to increase the carbon and nitrogen loads to receiving downstream waters. Primary production was not controlled by secondary production even if both were stimulated by agriculture. Instead, we found that higher secondary production in agricultural streams was due to reduced predation pressure following changes in fish communities. To which extent altered fish communities also triggered a trophic cascade with changes in organic matter fluxes and altered trophic interactions will be evaluated. The response of traditional indicators to agriculture was as high as that of ecosystem functioning but the significance of changes for the entire ecosystem is unclear. We suggest that limitations can be overcome if traditional indicators are related to functional indicators. In order to implement the knowledge gathered with HECTARE into catchment management measures, the following three points need to be addressed in future projects. First, agricultural streams are multiple stressed ecosystems and we now need a thorough understanding of the impact of the individual drivers associated with agriculture. This requires factorial experiments applied at least at the mesocosm-scale, where unique and interacting effects of drivers such as fine sediments and nutrients on ecosystem functioning are tested. Second, we need a better understanding of the response of ecosystem functions along driver gradients. Studying the development of ecosystem functioning along gradient of increasing driver intensity allows for deriving thresholds at which functioning exceeds critical points. This can be used to inform catchment management in order to establish critical limits and safety margins for relevant drivers. Finally, projects testing the reversibility of human impacts are needed in order to quantify if impacts of agricultural land use can be restored with ecosystem functions returning to pristine levels. In conclusion, HECTARE successfully combined a whole-ecosystem approach combined with a functional perspective and provided novel insights into how agricultural land use directly and indirectly impacts the multifunctionality and biodiversity of streams. The knowledge gathered with HECTARE did not only deepen the understanding on how humans alter functional attributes of ecosystems but also provided the basis for future studies implementing basic knowledge into stream and river management.
Publications
- (2013): An inter-biome approach to assess the impacts of agricultural land use on stream ecosystem functioning. - Symposium for European Freshwater Sciences (SEFS), Münster, Germany
Wild, R., Parlow, L., Norf, H. & Brauns, M.
- (2014): Biofilmfunktion und -struktur zur Bewertung von Effekten von Landnutzung auf Fließgewässerökosysteme. - Annual meeting of the German Limnological Society, Magdeburg, Germany
Parlow, L., Brauns, M., Wild, R. & Norf, H.
- (2015): Beyond nitrate: Developing multiisotopic approaches to quantify the fate and transport of nitrogen within catchments. - IAEA International Symposium on Isotope Hydrology, Vienna, Austria
Wells, N.S., Knöller, K., Fenton, O., Clagnan, E. & Brauns, M.
- (2015): Reactivity of dissolved organic nitrogen during downstream transport. - 20th European Nitrogen Cycle Meeting, Aberdeen, UK
Wells, N.S. & Brauns, M.
- (2016): Land use effects on dynamics and composition of particulate organic matter in temperate headwater streams. - Annual meeting of the German Limnological Society, Vienna, Austria
Wild, R., Gücker, B., Weitere, M. & Brauns, M.
- (2017): Agricultural land use reduces in-stream retention of terrestrial dissolved organic carbon. - ASLO Aquatic Sciences Meeting, Hawaii, USA
Brauns, M., Kamjunke, N., Neu, T.R., Norf, H., Wells, N.S., Wild, R. & Gücker, B.
- (2018): Tandem action of natural and chemical stressors in stream ecosystems: insights from a population genetic perspective.- Environmental Science & Technology 52: 7962-7971
Inostroza, P.A., Vera-Escalona, I., Wild, R., Norf, H & Brauns, M.
(See online at https://doi.org/10.1021/acs.est.8b01259)
