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Abstract. Livestock manure nitrogen (N) and phosphorus (P) play an importantrole in biogeochemical cycling. Accurate estimation of manure nutrient isimportant for assessing regional nutrient balance, greenhouse gas emission,and water environmental risk. Currently, spatially explicit manure nutrientdatasets over a century-long period are scarce in the United States (US).Here, we developed four datasets of annual animal manure N and P productionand application in the contiguous US at a 30 arcsec resolution overthe period of 1860–2017. The dataset combined multiple data sourcesincluding county-level inventory data as well as high-resolution livestockand crop maps. The total production of manure N and P increased from 1.4 Tg N yr−1 and 0.3 Tg P yr−1 in 1860 to 7.4 Tg N yr−1 and 2.3 Tg P yr−1 in 2017, respectively. The increasing manure nutrient productionwas associated with increased livestock numbers before the 1980s andenhanced livestock weights after the 1980s. The manure application amountwas primarily dominated by production, and its spatial pattern was impactedby the nutrient demand of crops. The intense-application region mainlyenlarged from the Midwest toward the southern US and became moreconcentrated in numerous hot spots after the 1980s. The South Atlantic–Gulf and Mid-Atlantic basins were exposed to high environmental risks due to theenrichment of manure nutrient production and application from the 1970s tothe period of 2000–2017. Our long-term manure N and P datasets providedetailed information for national and regional assessments of nutrientbudgets. Additionally, the datasets can serve as the input data forecosystem and hydrological models to examine biogeochemical cycles interrestrial and aquatic ecosystems. Datasets are available at https://doi.org/10.1594/PANGAEA.919937 (Bian etal., 2020). 

Abstract. Water management substantially alters natural regimes ofstreamflow through modifying retention time and water exchanges amongdifferent components of the terrestrial water cycle. Accurate simulation ofwater cycling in intensively managed watersheds, such as the Yakima River basin (YRB) in the Pacific Northwest of the US, faces challenges inreliably characterizing influences of management practices (e.g., reservoiroperation and cropland irrigation) on the watershed hydrology. Using the Soiland Water Assessment Tool (SWAT) model, we evaluated streamflow simulationsin the YRB based on different reservoir operation and irrigation schemes.Simulated streamflow with the reservoir operation scheme optimized by theRiverWare model better reproduced measured streamflow than the simulationusing the default SWAT reservoir operation scheme. Scenarios with irrigationpractices demonstrated higher water losses through evapotranspiration (ET)and matched benchmark data better than the scenario that only consideredreservoir operations. Results of this study highlight the importance ofreliably representing reservoir operations and irrigation management forcredible modeling of watershed hydrology. The methods and findings presentedhere hold promise toenhance water resources assessment that can be applied to other intensively managed watersheds. 

The biogeochemical processes of carbon (C), nitrogen (N), and phosphorous (P) are fully coupled in the Earth system, which shape the structure, functioning, and dynamics of terrestrial ecosystems. However, the representation of P cycle in terrestrial biosphere models (TBMs) is still in an early stage. Here we incorporated P processes and C‐N‐P interactions into the C‐N coupled Dynamic Land Ecosystem Model (DLEM‐CNP), which had a major feature of the ability in simulating the N and P colimitation on vegetation C assimilation. DLEM‐CNP was intensively calibrated and validated against daily or annual observations from four eddy covariance flux sites, two Hawaiian sites along a chronosequence of soils, and other 13 tropical forest sites. The results indicate that DLEM‐CNP significantly improved simulations of forest gross and net primary production (R²: 0.36–0.97, RMSE:1.1–1.49 g C m⁻² year⁻¹for daily GPP at eddy covariance flux sites;R² = 0.92, RMSE = 176.7 g C m⁻² year⁻¹for annual NPP across 13 tropical forest sites). The simulations were also consistent with field observations in terms of biomass, leaf N:P ratio and plant response to fertilizer addition. A sensitivity analysis suggests that simulated results are reasonably robust against uncertainties in model parameter estimates and the model was very sensitive to parameters of P uptake. These results suggest that incorporating P processes and N‐P interaction into terrestrial biosphere models is of critical importance for accurately estimating C dynamics in tropical forests, particularly those P‐limited ones.

 

Insufficiently calibrated forest parameters of the Soil & Water Assessment Tool (SWAT) may introduce uncertainties to water resource projections in forested watersheds. In this study, we improved SWAT forest parameterization and phosphorus cycling representations to better simulate forest ecosystems in the St. Croix River basin, and we further examined how those improvements affected model projections of streamflow, sediment, and nitrogen export under future climate conditions. Simulations with improved forest parameters substantially reduced model estimates of water, sediment, and nitrogen fluxes relative to those based on default parameters. Differences between improved and default projections can be attributed to the enhanced representation of forest water consumption, nutrient uptake, and protection of soil from erosion. Better representation of forest ecosystems in SWAT contributes to constraining uncertainties in water resource projections. Results of this study highlight the importance of improving SWAT forest ecosystem representations in projecting delivery of water, sediment, and nutrients from land to rivers in response to climate change, particularly for watersheds with large areas of forests. Improved forest parameters and the phosphorus weathering algorithms developed in this study are expected to help enhance future applications of SWAT to investigate hydrological and biogeochemical consequences of climate change.