Macrophytes enhance reach-scale metabolism on a daily, seasonal and annual basis in agricultural lowland streams

Data-Driven System Dynamics Model for Simulating Water Quantity and Quality in Peri-Urban Streams

“…Alternatively, and considering the continuous overestimation in the summer period for all associated sampling periods, a diffuse release from phosphorous stored in the streambed sediments in the summertime cannot be excluded. Such processes have been observed and described in lentic environments [85], but also in streams where phosphorous becomes available by desorption and fueled by enhanced decomposition of organic matter and lower oxygen levels at higher temperatures [56,86]. P-release from the sediment in the urban stream environment has also been documented when coupled with low DO concentrations ( [87]), although often in connection with lower NO 3 concentrations compared to the present study.…”

“…DO in the stream is depleted by carbonaceous biological oxygen demand (cBOD, Equation (A37)), nitrification (NBOD, Equation (A43)), a constant "background" sediment oxygen demand (SOD, Equation (A54)), and an additional dynamic heterotrophic respiration term (Equation (A72)). This term accounts for enhanced heterotrophic activities, stemming from enhanced settling of fine organic matter or plant exudation in streams with a high density of water plants, as highlighted in [56]. DO is also affected by photosynthesis/autotrophic plant respiration (Equations (A68)-(A72)) and balanced by a reaeration process.…”

“…Several studies highlighted that urbanization leads to increased and highly dynamic loads of more labile dissolved organic matter fraction and enhanced heterotrophic respiration [93,94], which will constitute a challenge in peri-urban settings considering the myriad of delivery pathways. Another possible driving mechanism could be algae blooms phenomena followed by settling and decomposition (as discussed in Section 4.2.2) or aquatic plant biomass, with macrophytes strongly affecting the local flow conditions, resulting in flow velocity reduction, fine sediment accumulation, and ultimately, enhanced metabolism in lowland streams, as shown in [56] for another small shallow stream. To this day, the modeling of this type of interaction and understanding of heterotrophic respiration is still limited (but see [95] and a coupled model of stream metabolism and microbial biomass, calibrated on long-term monitoring series ) and constitute an important source of uncertainty for any DO simulation in water quality models [82].…”

“…The simulations revealed, for example, an underestimation of phosphorus concentrations compared to the observed data. While unknown sources such as agricultural drainage or septic tanks cannot be excluded in peri-urban catchments and should be investigated further, several studies pointed out an enhanced release of reactive and legacy phosphorus in summer periods under low DO conditions for both mixed and single land-use streams [56,85,87]. Such a process can become an important feedback mechanism.…”

Vegetation and Residence Time Interact to Influence Metabolism and Net Nutrient Uptake in Experimental Agricultural Drainage Systems

“…Unaccounted for uptake and storage may help to explain strong patterns of enhanced GPP and ER coupled with weaker nutrient storage patterns within vegetated systems. However, macrophyte cover has been shown to enhance GPP and ER rates and contribute proportionally more to ecosystem metabolism than other plant forms; moreover, plant biomass and chlorophyll a have been found to explain the majority of variation in daily GPP (80%) and ER (63%) in agricultural streams [70,71]. Additionally, C assimilation and processing via metabolic processes require nutrient inputs; plant and associated microbial uptake can be a significant nutrient removal mechanism in vegetated aquatic systems [42].…”