Poor water source sink relationship within chalk streams, implications for ecosystem structureand function.IntroductionThe ecosystem consists of living organisms (biotic compound), their habitat (abiotic compound), andexchanges, transformations of matter and energy between them.
The combination of biotic and abiotic aspectsof an ecosystem produces the structure of the ecosystem, where the energy and nutrient flow is a function ofthe ecosystem. Ecosystem structure is the main aspect in order to maintain healthy ecosystem function andproviding good services for all living organisms.Rivers make up only 0.
01% of all Earth’s water budget. Despite this, the importance of lotic ecosystem on aglobal scheme is highly valuable. Because of hydrological connectivity, rivers and streams are fundamentalfor global water cycle; flowing water provide pathways for biogeochemical exchange within aquatic andterrestrials ecosystems, unifies water bodies and oceans.
Due to its dynamics, a lotic ecosystem is sculptingsurface, creating habitats and, being strongest erosion agent, provides geochemical materials to all systems.Having that in mind, undergoing processes within fluvial ecosystems has a major impact not only on the scaleof particular river system but also has an overall, global importance. A lotic system has to benefits forhumans: direct exploitation of rivers (food, fresh water, etc.) and indirect (climat change, temperature control,etc.), by providing nutrients and organic matter to terrestrial systems, in order to maintain healthybiodiversity which sustains a healthy environment for humanity (Cardinale et al.
, 2012).Like within all ecosystems, the main function of rivers and streams are energy transportation and nutrientturnover. Although, due to hydrological connectivity the processes within a fluvial structure, riverfunctioning is tightly related with a surrounding terrestrial structure. Autochthonous, allochthonous subsidies,processing and retaining organic matter; all combined, creates a complex, unified functioning system, wherethe flowing water is highly important.
The differences in physical characteristics, such as river flow and depth are supporting heterogeneousenvironment within an ecosystem. Flow is one of the factors to determine primary features of the river bed(sediment granulometry, deposition of sediment and organic matter, oxygen concentration, etc.), whichunderpin primary conditions for fauna and flora communities. Combination of abiotic and biotic structurewithin the habitat, maintain ecosystem functioning in a different way; production and respiration, nutrient andenergy flow, all this function are dependent on the structural aspects of the ecosystem.The river Cray was surveyed as a model system in order to understand, how differences of underlyingecosystem structure supports differences in the functioning of an ecosystem. The heterogeneity within the river Cray is visually noticeable; three different patch types (microhabitats)were surveyed: submerged- mostly covered by macrophytes, area with relatively slower flow, main channel –area of clean, open running water, mostly with an absence of macrophytes and higher flow over large calibersubstrate, marginal strip – areas closest to the bank of the river, depositional areas, with an increasingconcentration of sediment deposition, slowest water flow. The aim of the research is to see if the variationswithin ecosystem structure can lead to differences in function in order to provide ecosystem services.
Wefocused on measuring nutrients NO2-, NO3-, NH4+, and PO43-, in order to detect how a difference inmicrohabitat structure is supporting the provision of key nutrients, which maintain healthy ecosystemfunctioning to provide ecosystem services.MethodsStudy siteThe river Cray (latitude 51.424294; longitude 0.12654262) was chosen as a model system for this study. Theriver rises at natural ponds in Orpington are in Bromley, southern England.
The upstream catchment of theriver is very highly urban, here the river is modified and flow within artificial channels and culvert sections.Middle and downstream catchment are in a more natural territory, here the river flows through semi-naturalparkland in Footscray Meadows and Hall Place (Environmental Agency, 2017).