High-Frequency Monitoring Reveals Multiple Frequencies of Nitrogen and Carbon Mass Balance Dynamics in a Headwater Stream

The uptake of aquatic nutrients can represent a major pathway for their removal from river ecosystems and is a key control on nitrogen and carbon export from watersheds. Our understanding of temporal variability in nutrient mass balance is incomplete as conventional methods for estimating uptake rates are suited to low-frequency analysis. Here, we utilised hourly streamflow, nitrate (NO3--N) and dissolved organic carbon (DOC) to generate near-continuous estimates of nutrient uptake along a 1 km reach in a headwater catchment with a history of agricultural activity. We identified variability in nutrient mass balance at multiple frequencies. Over seasonal timescales, a shift from nitrate release during spring to uptake during autumn was apparent. In contrast, consistent uptake of DOC was observed across the whole monitoring period (i.e., spring—autumn). Both DOC and nitrate uptake were related significantly to environmental variables (river discharge) and antecedent discharge conditions. DOC:nitrate stoichiometry appeared to be a key control on nitrate uptake rates, yet this coupling weakened from summer to autumn as DOC became more abundant and physical controls become more important. Daily cycles in nutrient uptake were evident and at times the investigated reach acted as a net sink of DOC during the day and a source at night. Short-term impacts of storm events on uptake rates varied seasonally but no consistent changes were observed between pre- and post-event conditions, suggesting aquatic communities were resilient to short-term flow disturbances. For the duration of our study, the reach acted as net sink from the water for DOC (−1.7% of upstream flux) and a net source for nitrate (+2.6%). Even during autumn, when uptake was greatest, mass removal represented <3% of nitrate exported downstream. Our results facilitate new insights into multi-timescale patterns and drivers of stream ecosystem processes, which are essential for developing effective catchment-scale management strategies.

Treatment of Agricultural Drainage Water by Surface-Flow Wetlands Paired with Woodchip Bioreactors

Nutrient losses from agricultural fields have long been a matter of concern worldwide due to the ecological disturbance this can cause to surface waters downstream. In this paper a new design concept, which pairs a surface-flow constructed wetland (SFW) with a woodchip bioreactor (WB), was tested in relation to its capacity to reduce both nitrogen (N) and phosphorus (P) loads from agricultural tile drainage water. A nutrient mass balance and a comparative analysis were carried out together with statistical regressions in order to evaluate the performance of four SFW+WBs under different catchment conditions. We found marked variations between the systems in regard to hydraulic loading rate (0.0 to 5.0 m/day) and hydraulic retention time (1 to 87 days). The paired system worked as nutrient sinks throughout the study period. Total N and total P removal efficiencies varied from 8% to 51% and from 0% to 80%, respectively. The results support the use of the new design concept for nutrient removal from tile-drained agricultural catchments in Denmark as part of national management plans, with the added advantage that smaller areas are needed for construction (0.1% to 0.2% of the catchment area) in comparison to standalone and currently used SCWs (~1%).

370 Predicting nitrogen and phosphorous flows in beef open lots

This research summarizes a large existing data base collected over fifteen years to examine origin and fate of nitrogen and phosphorous in an open lot beef system, as impacted by seasonal changes, diets, and management practices. Data from 15 winter trials, including 200 pens, and 15 summer trials, including 216 pens were reviewed for nutrient mass balance, which was then used to determine the correlations of season, diet, and management with nitrogen and phosphorous intake, retention, manure harvested, loss, and runoff. All relationships were evaluated using linear regression SAS. Results suggested N in harvested manure for winter and summer averaged 90 and 51 g/steer daily, respectively (compared to ASABE standard of 88.5) and P harvested in manure for winter and summer averaged 26 and 17.7 g/steer daily, respectively (compared to ASABE standard of 37.5). Results of this summary show that the amount of nitrogen lost and retained in the manure is correlated to season (winter versus summer feeding period). Nitrogen in the manure (R2=0.21) and amount lost (R2=0.65) correlations with N intake in the summer were greater compared to winter (R2=0.06) and (R2=0.22). There is a greater correlation of phosphorous intake with amount harvested in manure (R2=0.32) in the winter versus the summer (R2=0.19). Results of the mass balance data compared with ASABE standards suggest greater observed dietary nutrient intakes than assumed by these standards. For example, average winter and summer nitrogen intakes of 220 and 250 g/steer daily exceeds the ASABE standard of 192 g/steer daily. These unique data describe the variability of nutrient recovery and losses from beef systems—and the importance of basing standard planning estimates on dietary concentration and evolving with current practices.

Nutrient Mass Balance and Fate in Dairy Cattle Lots with Different Surface Materials

On dairy farms, outdoor lots where cows spend substantial time can be areas of high nutrient deposition in manure. This represents an inefficient use of farm nutrients, if the nutrients are not recovered, and a potential for nutrient loss to the environment. Management of barnyards to recover nutrients can have environmental and production benefits. We monitored nitrogen (N) and phosphorus (P) fate for five years in dairy heifer barnyard plots constructed with soil, sand, or bark mulch surfaces. The plots were stocked with heifers several times per year for about a week at a time. We monitored N and P loss in runoff (soil plots only), leachate, and gas emissions. Of the total N inputs to the plots through heifer excretion, 6% to 8% of inputs were lost in runoff (~2%), leachate (~3% to 4%), and gas emissions (~3% to 4%) from the soil and mulch plots. Most of the N inputs remained in the surface materials. For the sand plots, more N inputs were lost in leachate (~13%) and gas emissions (~6%), but most of the N remained in the surface material. Of total P inputs to the plots through heifer excretion, 4% to 6% of inputs were lost in runoff and leachate, with most of the P remaining in the surface materials. The results suggest that most of the nutrients deposited by heifers onto barnyards could be recovered and used as fertilizer for crop growth by excavating the surface materials and spreading them on cropland, by including animal holding areas in land used for crop rotation so crops can recover nutrients , or by corralling animals directly on cropland. Keywords: Barnyards, Cattle, Leaching, Nutrients, Runoff.

Food web and ecological models used to assess aquatic ecosystems submitted to aquaculture activities

ABSTRACT: Continental aquatic ecosystems play a fundamental role in economic and social development; however, they are vulnerable to environmental degradation due to the various stresses to which they are submitted. Aquaculture is among the main anthropic activities that influence these environments. Mathematical modelling of aquatic ecosystems performed using a set of computational tools allows simplified representation of environment regarding its biotic and abiotic components. Some of the most used techniques are: hydrodynamic modelling, focusing on the dispersion of nutrients; nutrient-mass balance modelling, especially phosphorus; bioenergetic modelling in animal production systems, with an estimate of the generation of residues in the environment by farmed animals; and trophic and ecological modelling, focusing on aquatic communities and their interactions. These techniques help understand changes caused by aquaculture systems in aquatic environments. In this way, it is possible to estimate the magnitude and extent of the impacts of these activities by simulating the possible environmental changes over time. It can be concluded that techniques involving mathematical modelling can provide relevant information for future impacts prediction on aquatic environments, promoting the management of water resources and their multiple uses.

24-hour nutrient mass balance of small storage reservoir included in municipal rainwater drainage system

The paper presents the results of research, which aimed at tracing the quantitative and qualitative effect of the ”Tomaszowska” urban retention reservoir (located in the Łódź city) on the Olechówka River flowing through it over a period of one day. For this purpose, two measurement-control points were established located directly above the inflow of river to the reservoir, and below the weir. Hydrological and hydrochemical measurements were performed every two hours. Results obtained in this research present the reservoir as an object that in terms of the inflowing river, among others, in a daily balance of pollutants retains mineral and biogenic compounds, and releases dissolved and suspended organic compounds, and also changes the structure of pollution (in the case of total dissolved solids and total nitrogen, increasing the contribution of their organic forms).

Quantifying dairy farm nutrient fluxes and balances for improved assessment of environmental performance

Excess nutrients are challenging the long-term sustainability of grazing-based dairy farming. Whole-farm nutrient-mass balance (NMB) is a well recognised approach to improve on-farm nutrient management decisions. In the present paper, we use a standardised approach for quantifying NMB on grazing-based dairy farms, using a newly developed online tool. Preliminary evaluation, using selected farm data from a previous Australia-wide dairy-farm nutrient study, demonstrated highly comparable estimates of farm area, nutrient fluxes and NMB, with substantial efficiencies in time and sample analysis. Nutrient mass balances were also determined on 16 diverse dairy farms across the five major dairy regions of Victoria, Australia. These results highlighted the importance of purchased feed, fertiliser and milk sales, as major sources of nutrient inputs and outputs, with whole-farm NMB for the 16 dairy farms ranging from 185 to 481 kg/ha for nitrogen, 12–59 kg/ha for phosphorus, 9–244 kg/ha for potassium and –6–55 kg/ha for sulfur. Current industry adoption of the NMB tool has confirmed the benefits of a standardised and efficient collation and processing of readily available farm data to inform nutrient management decisions on commercial dairy farms. We suggest that the standardised assessment of nutrient fluxes, balances and efficiency, as well as feed- and milk-production performance at the whole-farm level, provides dairy farmers, farm advisors and industry and policy analysts with the ability to determine industry-wide goals and improve environmental performance.