TY - JOUR A1 - Jäger, Christoph G. A1 - Borchardt, D. T1 - Longitudinal patterns and response lengths of algae in riverine ecosystems: A model analysis emphasising benthic-pelagic interactions JF - Journal of Theoretical Biology N2 - In riverine ecosystems primary production is principally possible in two habitats: in the benthic layer by sessile algae and in the surface water by planktonic algae being transported downstream. The relevance of these two habitats generally changes along the rivers' continuum. However, analyses of the interaction of algae in these two habitats and their controlling factors in riverine ecosystems are, so far, very rare. We use a simplified advection-diffusion model system combined with ecological process kinetics to analyse the interaction of benthic and planktonic algae and nutrients along idealised streams and rivers at regional to large scales. Because many of the underlying processes affecting algal dynamics are influenced by depth, we focus particularly on the impact of river depth on this interaction. At constant environmental conditions all state variables approach stable spatial equilibria along the river, independent of the boundary conditions at the upstream end. Because our model is very robust against changes of turbulent diffusion and stream velocity, these spatial equilibria can be analysed by a simplified ordinary differential equation (ode) version of our model. This model variant reveals that at shallower river depths, phytoplankton can exist only when it is subsidised by detaching benthic algae, and in turn, at deeper river depths, benthic algae can exist only in low biomasses which are subsidised by sinking planktonic algae. We generalise the spatial dynamics of the model system using different conditions at the upstream end of the model, which mimic various natural or anthropogenic factors (pristine source, dam, inflow of a waste water treatment plant, and dilution from e.g. a tributary) and analyse how these scenarios influence different aspects of the longitudinal spatial dynamics of the full spatial model: the relation of spatial equilibrium to spatial maximum, the distance to the spatial maximum, and the response length. Generally, our results imply that shallow systems recover within significantly shorter distances from spatially distinct disturbances when compared to deep systems, independent of the type of disturbance. KW - Nutrients KW - Light KW - Longitudinal gradient KW - Resilience Y1 - 2018 UR - https://doi.org/10.1016/j.jtbi.2018.01.009 VL - 442 SP - 66 EP - 78 ER - TY - JOUR A1 - Jäger, Christoph G. A1 - Diehl, S. T1 - Resource competition across habitat boundaries: asymmetric interactions between benthic and pelagic producers JF - Ecological Monographs N2 - In shallow aquatic systems, benthic and pelagic primary producers typically compete for light and nutrients along opposing vertical supply axes: pelagic algae shade the benthic habitat; conversely, benthic algae intercept the nutrient flux from the sediment to the pelagic habitat. We present a general framework for analyzing such spatially asymmetric resource competition across habitat boundaries using a mechanistic, dynamical model. We visualize the mechanisms determining the outcome of these cross‐habitat interactions using zero‐net‐growth isoclines, resource supply points, and resource consumption vectors. In extensive invasion analyses, we characterize the abiotic and competitive persistence boundaries of pelagic and benthic primary producers, which are set by environmental factors determining nutrient and light supply and are modified by resource use by the competitor in the respective other habitat. We note several qualitative differences between cross‐habitat and “classical” within‐habitat resource competition. First, coexistence of cross‐habitat competitors is facilitated by, but does not require niche differentiation with respect to, the utilization of resources. Because each species has a competitive edge for the resource that is supplied from “its” side of the system, a competitor that is inferior in utilizing both resources can sometimes coexist with, or even exclude, a superior competitor. Second, increasing the external supply of one resource (the nutrient) may initially favor both competitors, until a breakpoint is reached where the benthic producer goes abruptly extinct. Finally, whether a given pair of cross‐habitat competitors coexist or shows alternative states may depend on the environment. Specifically, benthic and pelagic algae may coexist at low nutrient and light supply but produce alternative states at high nutrient and light supply. Alternative states are, in turn, promoted by any algal trait combination that increases the spatial asymmetry in resource consumption, i.e., leads to a higher nutrient consumption in the benthic habitat and/or a higher light consumption in the pelagic habitat. In a first empirical application, we show that predictions from our model give a good fit to published data on benthic and pelagic primary production in temperate and arctic lakes spanning a broad range of nutrient environments. KW - Benthic algae KW - Consumption vector KW - Light KW - Meta-ecosystem KW - Nutrients KW - Pelagic algae KW - Resource competition KW - Spatial subsidies KW - Supply point KW - trait values Y1 - 2014 UR - https://doi.org/10.1890/13-0613.1 VL - 84 IS - 2 SP - 287 EP - 302 ER - TY - JOUR A1 - Kamjunke, N. A1 - Büttner, O. A1 - Jäger, Christoph G. A1 - Marcus, H. A1 - von Tümpling, W. A1 - Halbedel, S. A1 - Norf, H. A1 - Brauns, M. A1 - Baborowski, M. A1 - Wild, R. A1 - Borchardt, D. A1 - Weitere, M. T1 - Biogeochemical patterns in a river network along a land use gradient JF - Environmental Monitoring and Assessment N2 - The Bode catchment (Germany) shows strong land use gradients from forested parts of the National Park (23 % of total land cover) to agricultural (70 %) and urbanised areas (7 %). It is part of the Terrestrial Environmental Observatories of the German Helmholtz association. We performed a biogeochemical analysis of the entire river network. Surface water was sampled at 21 headwaters and at ten downstream sites, before (in early spring) and during the growing season (in late summer). Many parameters showed lower concentrations in headwaters than in downstream reaches, among them nutrients (ammonium, nitrate and phosphorus), dissolved copper and seston dry mass. Nitrate and phosphorus concentrations were positively related to the proportion of agricultural area within the catchment. Punctual anthropogenic loads affected some parameters such as chloride and arsenic. Chlorophyll a concentration and total phosphorus in surface waters were positively related. The concentration of dissolved organic carbon (DOC) was higher in summer than in spring, whereas the molecular size of DOC was lower in summer. The specific UV absorption at 254 nm, indicating the content of humic substances, was higher in headwaters than in downstream reaches and was positively related to the proportion of forest within the catchment. CO2 oversaturation of the water was higher downstream compared with headwaters and was higher in summer than in spring. It was correlated negatively with oxygen saturation and positively with DOC concentration but negatively with DOC quality (molecular size and humic content). A principle component analysis clearly separated the effects of site (44 %) and season (15 %), demonstrating the strong effect of land use on biogeochemical parameters. KW - TERENO KW - Land use KW - Nutrients KW - Heavy metals KW - DOC KW - Bode Y1 - 2013 UR - https://doi.org/10.1007/s10661-013-3247-7 VL - 185 IS - 11 SP - 9221 EP - 9236 ER -