Nutrient Export Research Articles

Biochar as a water protection tool in peatland forestry – nutrient recovery from runoff water

Water quality is significantly affected by the forest logging activities that are carried out in drained peatlands, which causes a notable enhancement in sediment loading and nutrient export to water bodies. Furthermore, the seasonal fluctuations in nutrient concentrations in the runoff further underscore the need for efficient water protection tools in peatland forestry. To address these issues, biochar-based adsorption methods can potentially offer an effective alternative for water protection in peatland forestry. The current thesis investigates the potential for adsorption-based nutrient recovery from clear-cut peatland runoff water using Norway spruce and Silver birch biochars. In particular, the aim is to i) study the adsorption characteristics in relation to biochar properties and nutrient compounds in runoff waters in a small-scale laboratory experiment (Paper I); ii) investigate the adsorption characteristics of nitrogen (N) compounds from runoff water in a meso-scale laboratory experiment that utilises biochar reactors (Paper II); and iii) investigate the dynamics of biochar adsorption and desorption under fluctuating total nitrogen (TN) concentrations in runoff water (Paper III). Biochar made from birch and spruce were shown to efficiently adsorb N compounds from the water. Across all experiments, the TN content declined significantly, irrespective of the scale, or whether the runoff volume ranged from litres (I and III) to hundreds of litres (II). Furthermore, the TN content at the beginning of the experiment declined at the fastest rate. The results indicate that cases of relatively low adsorption capacity were attributed to the low initial TN concentrations in the water. In addition, TN adsorption occurs above a threshold concentration in natural runoff water. The spruce did not adsorb TN when the concentrations in the runoff water fell below 0.4 mg L-1. In this thesis, biochar emerges as a compelling water protection solution, particularly in regions where clear-cut peatlands release substantial quantities of nutrients.

Produtividade e exportação de nutrientes em um consórcio de milho e gramíneas forrageiras nas condições do semiárido

ABSTRACT The aim was to evaluate the productive performance and nutrient export of maize intercropped with drought-tolerant forage grasses. The experimental design was a randomized blocks in a 2x2x2+1 factorial scheme (two forage grasses species – Massai and Buffel; two forage sowing methods - in the furrow and broadcast; and two forage sowing times - anticipated and simultaneous; and monoculture maize as an additional control), with three replicates. The maize+forage intercropping promoted greater competition for resources, especially water, limiting N uptake, chlorophyll synthesis, and biomass production by maize under semiarid conditions. Early sowing gave forage plants a competitive advantage, favoring forage establishment before or immediately after the sowing of maize. Thus, the simultaneous sowing of forage grasses in a semiarid environment is a more appropriate option considering the importance of high levels of chlorophyll to ensure high photosynthetic activity in maize plants and greater capacity of biomass synthesis. Massai intercropped with maize exhibits a greaterpotential for biomass production than Buffel under semiarid conditions. Maize+Buffel result in highest macronutrient export by maize, while maize+Massai result in highest macronutrient exports by total forage biomass under a semiarid environment. The choice of the forage species and its sowing time in relation to maize are the main determinants of successful intercropping systems under semiarid conditions.

Biochar as a water protection tool in peatland forestry – nutrient recovery from runoff water

Water quality is significantly affected by the forest logging activities that are carried out in drained peatlands, which causes a notable enhancement in sediment loading and nutrient export to water bodies. Furthermore, the seasonal fluctuations in nutrient concentrations in the runoff further underscore the need for efficient water protection tools in peatland forestry. To address these issues, biochar-based adsorption methods can potentially offer an effective alternative for water protection in peatland forestry. The current thesis investigates the potential for adsorption-based nutrient recovery from clear-cut peatland runoff water using Norway spruce and Silver birch biochars. In particular, the aim is to i) study the adsorption characteristics in relation to biochar properties and nutrient compounds in runoff waters in a small-scale laboratory experiment (Paper I); ii) investigate the adsorption characteristics of nitrogen (N) compounds from runoff water in a meso-scale laboratory experiment that utilises biochar reactors (Paper II); and iii) investigate the dynamics of biochar adsorption and desorption under fluctuating total nitrogen (TN) concentrations in runoff water (Paper III). Biochar made from birch and spruce were shown to efficiently adsorb N compounds from the water. Across all experiments, the TN content declined significantly, irrespective of the scale, or whether the runoff volume ranged from litres (I and III) to hundreds of litres (II). Furthermore, the TN content at the beginning of the experiment declined at the fastest rate. The results indicate that cases of relatively low adsorption capacity were attributed to the low initial TN concentrations in the water. In addition, TN adsorption occurs above a threshold concentration in natural runoff water. The spruce did not adsorb TN when the concentrations in the runoff water fell below 0.4 mg L-1. In this thesis, biochar emerges as a compelling water protection solution, particularly in regions where clear-cut peatlands release substantial quantities of nutrients.

Nitrate isotope investigations reveal future impacts of climate change on nitrogen inputs and cycling in Arctic fjords: Kongsfjorden and Rijpfjorden (Svalbard)

Abstract. Ongoing climate change in the Arctic has caused tidewater glaciers to retreat while increasing the discharge of freshwater and terrestrial material into fjords. This can affect both nutrient inputs and cycling within the fjord systems. In particular, tidewater glaciers and the presence of associated subglacial meltwater plumes can have a large impact on fjord circulation and biogeochemistry. In this study, we assess the influence of tidewater glaciers on nitrogen inputs and cycling in two fjords in Svalbard during the summer using stable isotopic analyses of dissolved nitrate (δ15N and δ18O) in combination with nutrient and hydrographic data. Kongsfjorden receives inputs from tidewater glaciers, whereas Rijpfjorden mainly receives surface inputs from land-terminating glaciers. Results showed that both fjords are enriched in nutrients from terrestrial inputs. Nutrient ratios indicate excess Si and P relative to N. In both fjords, terrestrial nitrate from snowpack and glacier melting are identified as the dominant sources based on high δ18O-NO3- and low δ15N-NO3- of dissolved nitrate. In Kongsfjorden, mixed-layer nitrate is completely consumed within the fjord system, which we attribute to vigorous circulation at the glacial front influenced by the subglacial plume and longer residence time in the fjord. This is in contrast to Rijpfjorden where nutrients are only partially consumed perhaps due to surface river discharge and light limitation. In Kongsfjorden, we estimate terrestrial and marine N contributions to the nitrate pool from nitrogen isotopic values (δ15N-NO3-), and this suggests that nearly half the nitrate in the subglacial plume (50 ± 3 %) and the water column (44 ± 3 %) originates from terrestrial sources. We show that terrestrial N contributes significantly to the regenerated N pool (63 %–88 %) within this fjord suggesting its importance in sustaining productivity here. Given this importance of terrestrial nutrient sources within the fjords, increase in these inputs due to climate change can enhance the fjord nutrient inventory, productivity and nutrient export offshore. Specifically, increasing Atlantification and warmer Atlantic Water will encourage tidewater glacier retreat and in turn increase surface discharge. In fjords akin to Rijpfjorden this is expected to foster more light limitation and less dynamic circulation, ultimately aiding the export of nutrients offshore contributing to coastal productivity. Climate change scenarios postulated for fjords such as Kongsfjorden include more terrestrial N-fuelled productivity and N cycling within the fjord, less vigorous circulation due to the retreat of tidewater glaciers, and the expansion of oxygen-depleted deep waters isolated by the sill.

Evaluation of Biogeochemical Changes in Channelized and Restored Portions of a Subtropical Floodplain

Floodplains are critically important ecosystems that provide a whole suite of ecosystem services, including nutrient and carbon sequestration, flood mitigation, water storage, and critical wildlife habitat. However, human modification of rivers and floodplains through channelization, artificial levee construction, reductions in the active floodplain area, and water management can significantly reduce the ecosystem function of river–floodplain systems. In this study, we evaluated the changes in the nutrient loading of the Kissimmee River floodplain during the restoration of the river–floodplain system. In addition to time-series loading analysis, we also evaluated soil nutrient concentrations across the lower portion of the Kissimmee River floodplain. During the 44-year nutrient loading time-series, the floodplain remained a nutrient exporter with changes in nutrient loading generally corresponding to both water quality (i.e., point source reductions) and hydrologic restoration activities in the watershed and Kissimmee River floodplain. During the study period, inputs of total phosphorus and total nitrogen loads from upstream either significantly increased or remained the same. In addition to external sources of nutrients, internal sources of nutrients from floodplain soils can also contribute to the total nutrient export from the system. These internal sources could be organic via the decomposition of organic matter or geologic from the original excavation of the canal and/or restoration backfilling. Soil nutrient concentrations vary between vegetative communities and landscape position and could be a significant source of phosphorus to the downstream system, which is plagued by eutrophic conditions. Therefore, as floodplain function in the Kissimmee River continues to be restored and managed, additional effort may be needed to address nutrient inputs and internal legacy nutrients.

Investigating relationships between climate controls and nutrient flux in surface waters, sediments, and subsurface pathways in an agricultural clay catchment of the Great Lakes Basin

Water quality within agricultural catchments is governed by management practices and climate conditions that control the transport, storage, and exchange of nutrients between components of the hydrologic cycle. This study aims to improve knowledge of nitrogen (N) and phosphorus (P) transport in low permeability agricultural watersheds by considering spatial and temporal trends of surface water nutrient concentrations in relation to hydroclimatic drivers, sediment quality, shallow hyporheic exchange, groundwater quality, and tile drain discharge over a 14-month field study in a clay hydrosystem of the Lake Huron basin, one of the five Great Lakes. Results found that events of varying magnitude and intensity enhanced nutrient release from overland flow and subsurface pathways. Tile drain discharge was found to be a consistent and elevated source of P and N to surface waters when flowing, mobilizing both diffuse nutrients from fertilizer application and legacy stores in the vadose zone. Surface water quality was temporally variable at the seasonal and event scale. Targeted sampling following fertilization periods, snowmelt, and moderate precipitation events revealed catchment wide elevated nutrient concentrations, emphasizing the need for targeted sampling regimes. Controls other than discharge magnitude and overland flow were found to contribute to peak nutrient concentrations, including internal nitrate loading, soil-snowmelt interaction, catchment wetness, and freeze thaw cycles. Sediments were found to store P in calcium minerals and have a high P storage capacity. Instream mechanisms such as sediment P fixation and hyporheic exchange may play a role in mediating surface water quality, but currently have no discernable benefit to year-round surface water nutrient concentrations. Best management practices need to focus on reducing sources of agricultural nutrients (e.g., field phosphorus concentrations and tile drain discharge loading) at the watershed scale to reduce nutrient concentrations and export in flashy clay catchments.

NUTRIENT REMOVAL BY OFF-SEASON GRAIN SORGHUM AS AFFECTED BY INTERCROPPING WITH RUZIGRASS AND FERTILIZATION LEVELS IN THE BRAZILIAN CERRADO

Sorghum is an off-season crop option in succession to soybean in the Cerrado region, but many producers underestimate the fertilization requirement, which can harm the productive performance of the system as a whole. Aiming to quantify the uptake and export of nutrients by grain sorghum, experiments were carried out in monocropping and intercropping with ruzigrass (Uroclhoa ruziziensis), with three levels of NPK fertilization (control without fertilization; maintenance fertilization; and maintenance + 30%). The experimental design was randomized blocks, with four replications. Sorghum plants were sampled at 33, 67 and 130 days after sowing, corresponding to the eight-leaf, flowering and physiological maturation development stages. The nutrient accumulation throughout the sorghum cycle and the respective extraction and export rates were calculated. Intercropping with ruzigrass reduces grain yield, but does not influence sorghum nutrient accumulation. Fertilization in soil with current high fertility increases biomass and nutrient accumulation, however, without any impact on grain yield. In off-season sorghum crop, nutrient uptake occurs mostly during the vegetative phase. Each ton of grain produced removes the equivalent of 14.5; 5.0; 3.5; 1.1 and 0.5 kg of N, P2O5, K2O, Mg and S, in addition to 2, 2, 25, 9 and 11 g of B, Cu, Fe, Mn and Zn, respectively. The potential for nutrient removal by grain sorghum cultivation is comparable to the patterns of the off-season maize crop, evidencing the importance of fertilization to replenish the amounts of nutrient exported.

Carbon footprint of dairy manure management chains in response to nutrient recovery by aerobic pre-treatment

Aerobic pre-treatment of liquid dairy manure has previously been reported as an effective nutrient export and emissions mitigation approach. The first objective of this study was to experimentally determine the optimal intermittent aeration ratio for nutrient recovery from liquid dairy manure through an on-site pilot-scale reactor to partially reduce the required energy for the aerobic process. The second objective was to theoretically investigate the total carbon footprints of direct manure spreading on croplands and permanent manure storage in open anaerobic lagoons in response to nutrient removal by the optimal determined intermittent aerobic treatment ratio. Four scenarios (S) were included; S1 was the traditional scenario of manure spread on croplands without the aerobic pre-treatment, S2 was the modified scenario of manure spread on croplands that included the aerobic pre-treatment, S3 was the traditional scenario of manure storage in lagoons, and S4 was the modified scenario of manure storage in lagoons that included the aerobic pre-treatment. The results showed that comparable nutrient removal efficiencies could be obtained with a 5:1 intermittent aeration ratio. Total nitrogen (TN) and total phosphorus (TP) were recovered were 41.5 ± 1.3% and 37.0 ± 4.0%, respectively, in ammonium sulfate and phosphorus-rich sludge, while 55.3 ± 1.4% of the chemical oxygen demand (COD) was removed. The estimated total carbon footprint for S1, S2, S3, and S4 were 24.4, 37.9, 45.3, and 45.9 kg CO2-eqton−1, respectively. However, the total carbon footprint of S2′ and S4′, which used renewable-based energy to run the reactor instead of fossil-based energy used in S2 and S4, were estimated to 29.5 and 37.5 kg CO2-eqton−1, respectively. Clearly, applying the aerobic pre-treatment increased the total carbon footprint of all cases except S4′, in which the total carbon footprint was mitigated by −17.2%. Accordingly, the aerobic pre-treatment is only recommended in the case of S4’ from a carbon footprint point of view although it is an effective nutrient recovery technology.

Hydroclimatic variability across the international Lake of the Woods watershed: Implications for nutrient export and climate sensitivity

Characterizing streamflow and relationships with climate and watershed characteristics is an essential first step in the design of any monitoring program to assess basin response to changes in land use or climate. This is especially true for the international Lake of the Woods watershed, where recurrent algae blooms have been associated with nutrient inputs from the watershed and climate warming. Here, we present a basin-wide hydroclimatic analysis within the sparsely monitored Canadian portion of the basin. Spatial and temporal patterns in climate and runoff were assessed across the two major geo-zones: the Precambrian ‘Shield zone’, dominated by bedrock, forests and lakes, and the poorly drained ‘Agassiz zone’ where ditching and drainage for agriculture have substantially enhanced the hydrologic connectivity. While climate conditions were consistent across the watershed, Agassiz basins were flashy, highly variable, and more seasonal compared with Shield rivers, likely due to the moderating effect of lake storage in the Shield region. Temperatures increased across the basin (1910–2010), and there was more rainfall and runoff during the ice-covered months (Nov-Mar), suggesting a shift toward earlier snowmelt. Marked seasonality and large swings in flow extremes at the Agassiz rivers suggest this region is particularly sensitive to hydroclimatic change and that frequent monitoring is needed to capture important periods of nutrient export like spring runoff and storm events. In contrast, substantial storage within the Shield landscape suggests this zone is more hydrologically ‘resilient’ to climate extremes and that water quality and quantity measurements can be less frequent.

Using processed fertilizers or composted poultry manure results in similar yields but contrasting nutrient budgets in organic cabbage production

Certified organic farmers who grow mixed vegetables often rely on composted manure as their primary nutrient source to build soil organic matter and long-term fertility, but this can result in excessive phosphorus inputs relative to processed organic fertilizers. We established a two-year experiment to compare two certified organic fertilizers − 13-0-0 (derived from hydrolyzed feather meal, meat meal, and blood meal) and 10-2-8 (same components as 13-0-0 in addition to bone meal and sulfate of potash) – and composted chicken manure added to provide 112 kg plant-available N ha−1 in organic cabbage production of Northern Florida. Crown diameter was highest with processed fertilizers in both years, whereas SPAD readings were highest with 13-0-0 in 2020. In both years, sap nitrate measured during the growing season was generally higher with processed fertilizers relative to the composted manure treatment. Marketable yield was highest with processed fertilizers for both years and nutrient concentrations at harvest were similar among treatments, except for nitrogen concentrations that were highest with 10-2-8 in 2021. Nutrient export generally followed differences in yields and was comparable for processed fertilizers and composted manure. Using composted manure resulted in large nutrient surpluses, as opposed to smaller surpluses for 10-2-8 and deficits of phosphorus and potassium for 13-0-0. Our results confirm that poultry manure composted directly onsite can result in comparable organic cabbage yields relative to processed fertilizers, although this resulted in important phosphorus surpluses when applied to meet crop N demand.

Lake operation optimization of nutrient exports: Application of phosphorus control in the largest subtropical lake in the United States

This paper presents Lake Operation Optimization of Nutrient Exports (LOONE), a Python-based model with three coupled modules: 1) a water balance module to simulate hydrology and operations, 2) a nutrient module to simulate phosphorus dynamics in the water column, and 3) an optimization tool to design optimal reservoir releases. We applied the model to Lake Okeechobee (Florida, USA), a shallow subtropical lake receiving and exporting excessive amounts of nutrients, while providing water supply, recreation, and flood control. We evaluated LOONE under historical operation schedules for model verification, and then designed optimal releases that minimized phosphorus exports into the two main distributaries of Lake Okeechobee. We found that P loads could decrease by 12–33% under optimal operations. The software package could be used to evaluate management decisions to help control water quality issues such as high nutrient exports and harmful algal blooms in Lake Okeechobee and reservoirs worldwide.

Modeling the Effectiveness of Sustainable Agricultural Practices in Reducing Sediments and Nutrient Export from a River Basin

Water pollution from unsustainable agricultural practices is a global problem that undermines human health and economic development. Sustainable agricultural practices have been considered to maintain global food production without compromising water quality and ecosystem health. However, the effectiveness of sustainable agricultural practices in reducing sediments and nutrient export and the combination of practices that will best achieve water quality objectives is still under-explored. In this study, we assess the effectiveness of sustainable agricultural practices in reducing sediments and nutrients export to rivers and determine the combination of practices that would allow the highest reductions of sediments and nutrients, using the Soil and Water Assessment Tool (SWAT) in a Portuguese river basin highly affected by agricultural pollution. SWAT was calibrated and validated for river discharge, sediments, phosphorous, and nitrate loads at the outlet of the basin, with a good agreement between simulated and observed values. The effects of filter strips, fertilizer incorporation, and conservation tillage were analyzed considering both individual and combined effects. Our study shows that sustainable agricultural practices can substantially reduce sediments and nutrients export from a river basin, with the highest average combined depletion of sediments, phosphorus, and nitrate export (25%) achieved when fertilizer incorporation, conservation tillage, and filter strips were implemented simultaneously. Additional studies exploring the effect of sustainable agricultural practices across a range of climate and watershed characteristics, as well as their capacity to deal with challenges related to climate change, will further improve our understanding of the effectiveness of sustainable agricultural practices.

Simulating the hydrological impacts of land use conversion from annual crop to perennial forage in the Canadian Prairies using the Cold Regions Hydrological Modelling platform

Abstract. The Red River is one of the largest contributing sources of discharge and nutrients to the world's 10th largest freshwater lake, Lake Winnipeg. Conversion of large areas of annual cropland to perennial forage has been proposed as a strategy to reduce both flooding and nutrient export to Lake Winnipeg. Such reductions could occur either via a reduction in the concentration of nutrients in runoff or through changes in the basin-scale hydrology, resulting in a lower water yield and the concomitant export of nutrients. This study assessed the latter mechanism by using the physically based Cold Regions Hydrological Modelling platform to examine the hydrological impacts of land use conversion from annual crops to perennial forage in a subbasin of the La Salle River basin in Canada. This basin is a typical agricultural subbasin in the Red River Valley, characterised by flat topography, clay soils, and a cold subhumid, continental climate. Long-term simulations (1992–2013) of the major components of water balance were compared between canola and smooth bromegrass, representing a conversion from annual cropping systems to perennial forage. An uncertainty framework was used to represent a range of fall soil saturation status (0 % to 70 %), which governs the infiltration to frozen soil in the subsequent spring. The model simulations indicated that, on average, there was a 36.5 ± 6.6 % (36.5 ± 7.2 mm) reduction in annual cumulative discharge and a 29.9 ± 16.3 % (2.6 ± 1.6 m3 s−1) reduction in annual peak discharge due to forage conversion over the assessed period. These reductions were driven by reduced overland flow 52.9 ± 12.8 % (28.8 ± 10.1 mm), increased peak snowpack (8.1 ± 1.5 %, 7.8 ± 1.6 mm), and enhanced infiltration to frozen soils (66.7 ± 7.7 %, 141.5 ± 15.2 mm). Higher cumulative evapotranspiration (ET) from perennial forage (34.5 ± 0.9 %, 94.1 ± 2.5 mm) was also predicted by the simulations. Overall, daily soil moisture under perennial forage was 18.0 % (57.2 ± 1.2 mm) higher than that of crop simulation, likely due to the higher snow water equivalent (SWE) and enhanced infiltration. However, the impact of forage conversion on daily soil moisture varied interannually. Soil moisture under perennial forage stands could be either higher or lower than that of annual crops, depending on antecedent spring snowmelt infiltration volumes.

Groundwater flow patterns in a coastal fen exposed to drainage, rewetting and interaction with the Baltic Sea

Low-lying coastal peatlands are unique ecosystems where water levels and salt input with seawater determine vegetation and greenhouse gas emissions, while the export of nutrients and carbon via submarine groundwater discharge influences biogeochemical processes in shallow coastal sediments. Anthropogenic interferences like drainage and diking strongly impact the water flow. This study aimed at understanding the hydrological system in a rewetted coastal fen typical for the southern Baltic Sea. Groundwater observation wells were installed both in the peat layer and underlying sands, and continuous readings of water levels and specific conductivities were combined with groundwater dating and major ion composition analyses. Apparent tritium–helium groundwater ages between 7 and more than 60 years in the shallow aquifer below the peat revealed a long memory of the system. Recharge through the peat layer was identified as a major source of groundwater from neon and helium isotopes in combination with water levels. Chloride concentrations showed a homogeneous fraction of 30 % sea water throughout the aquifer despite differing groundwater ages. Drainage ditches still affect groundwater flow today depending on the peat and aquifer thickness. Both nutrient-enriched, brackish, deeper groundwater and freshwater from the precipitation-fed dune dike discharge to the sea. We conclude that rewetting of coastal peatlands mainly affects the groundwater in the upper peat, with little impact on the underlying aquifer, and might revive submarine groundwater discharge and associated nutrient fluxes despite low hydraulic gradients.

Climatology and nutrient fluxes in the Tagus estuary: A coupled model application

Rivers are responsible for the main transport of nutrients from land to estuaries and coastal areas. Understanding the fate of these anthropogenic inputs and their impacts on estuaries and adjacent marine ecosystems is essential for the protection of coastal waters. Here, the 3D MOHID hydrodynamic model coupled with a biogeochemical model was used to determine seasonal nutrient fluxes between areas of the Tagus estuary. For this purpose, the estuary was divided into boxes, which allowed to evaluate nutrients (and phytoplankton) exchanges between areas, to identify source and sink zones, to estimate the amount of nutrients exported to the coastal zone adjacent to the estuary, and to understand the recycling capacity of this estuarine system. Globally, for all nutrients and seasons, the highest net fluxes were observed in the main and central body of the estuary. The differences observed in the flux budget for each box and for all nutrients are mostly related to variations in the seasonal abundance of phytoplankton, which is much higher in Spring/Summer than in the rest of the year due to the higher seawater temperature and irradiance. During these seasons the high temperatures also promoted the fast mineralization of organic matter along the water column and in the sediment. For all seasons, an export of nutrients and phytoplankton from upstream to downstream was observer at the surface, and from the most confined areas of the southern margin into the central body and main channel of the estuary, whilst the opposite was observed in the bottom layers. Nevertheless, surface fluxes were always higher than those recorded at depth, indicating that the estuary exported nutrients to the coast, all year round. For 2020 it was estimated that 52%, 88% and 65% of the ammonium, nitrate, and phosphate, respectively, that entered the estuary from both rivers and wastewater treatment plants were exported to the adjacent coast. The amount of nutrients exported to the coastal area is closely related to river discharge, being much higher in flood years than in dry years, particularly for nitrate.

Future projections of river nutrient export to the global coastal ocean show persisting nitrogen and phosphorus distortion

Nitrogen (N) and phosphorus (P) from anthropogenic sources are needed to produce food for the growing world population. As a result, these nutrients can be found in nearly every water body across the globe. Not only nutrient loading is important but also the molar ratio and its deviation from the “natural” Redfield ratio. Here we show that rivers, which have more than 50% anthropogenic sources and at the same time elevated N:P ratios (> 25) contributed 36% to the total global N export to coastal waters in 2015. The five Shared Socioeconomic Pathways (SSP) were used in combination with the Representative Concentration Pathways climate scenarios to project river nutrient loadings for 2050. Future nutrient export is projected to decline in high-income countries (with N:P ratios exceeding Redfield). In Brazil, India and China, however, a decline of N:P is only the case in a scenario oriented toward sustainable development (SSP1). The human-dominated river N and P export with elevated N:P ratios will increase in all SSPs, except in SSP1 where it stabilizes. Integrated strategies for both N and P considering all relevant trade-offs and societal sectors are urgently needed to reduce the nutrient pressure on surface waters.

Biomass partitioning and nutrient fluxes in Silphium perfoliatum and silage maize cropping systems

Cup plant cultivation as feedstock for anaerobic digestion has become an emerging topic in European Agriculture. Although there is a gap in methane yields between cup plant and the benchmark crop silage maize, cup plant as a perennial crop provides several ecological advantages. Amongst others, studies have proven its potential for carbon sequestration. With the present study, we addressed the gap in knowledge about biomass partitioning above- and belowground as well as recycling of organic matter and nutrients for cup plant and compared the results to silage maize. Therefore, a 2 year field experiment was conducted under practical conditions on rather shallow soil conditions in a low mountain landscape in Western Germany. Relevant plant fractions like litterfall, yield biomass and stubbles were collected continuously and analyzed for their nutrient contents. Results show that the cup plant is characterized by more than 2000 kg ha− 1 a− 1 of pre-harvest losses with a high palatability. In sum, only 77% of the grown cup plant biomass can be harvested in contrast to 96% of silage maize. Thus, an intense, element-specific nutrient recycling takes place in cup plant whereas this is negligible in silage maize. Furthermore, clearly different, element-specific nutrient exports with yield were highlighted. In cup plant, exports were distinctly lower for nitrogen but several times higher for calcium compared to silage maize. Cup plant also showed 36% more roots with higher root masses particularly in the subsoil.Graphical abstract

Drought impacts on hydrology and water quality under climate change

The Intergovernmental Panel on Climate Change (IPCC) has predicted that droughts are projected to affect global hydrology and water quality in varying ways, resulting in a considerable challenge to water availability for society, environment, and ecosystems. This study employed the Soil and Water Assessment Tool to evaluate how drought affects hydrology and water quality in the Miyun Reservoir watershed, coupled with bias-corrected climate projections in the Representative Concentration Pathway 8.5 scenario, accommodating the intercoupling effects of precipitation shifts and rising temperatures. The standardized precipitation index (SPI), standardized runoff index (SRI), and standardized soil moisture index (SSWI) were used to characterize meteorological, hydrological, and agricultural droughts that occur in the different phases in the hydrological cycle. Climate change had the most significant impact on agricultural drought. SSWI were projected to considerably increase in intensity, frequency, and duration in most subbasins by up to 15 %, 55 %, and 45 %, respectively, and showed a strong correlation with meteorological and hydrological droughts (correlation coefficients r = 0.54, 0.57, and 0.60 with SPI for the baseline, near future and far future periods, and 0.91, 0.87, and 0.89 with SRI for the three periods, respectively). Hydrological components, sediment export, and nutrient loss were highly correlated with changes in drought indexes, with r ranging between −0.68 and 0.34 in the near future period and −0.62 and 0.53 in the far future period. Drought conditions of surface runoff and soil water dominated the changes in sediment export, and hydrological drought was the major cause for reduced nutrient loads. In addition to drought impacts, the synergistic effects of increasing precipitation and rising temperature led to a certain degree of increase in sediment and nutrient exports. The results of this study emphasize the need to enhance the resilience of watershed systems to the predicted increases in the intensity, frequency, and duration of droughts.

Yukon River incision drove organic carbon burial in the Bering Sea during global climate changes at 2.6 and 1 Ma

Abstract. River erosion affects the carbon cycle and thus climate by exporting terrigenous carbon to seafloor sediment and by nourishing CO2-consuming marine life. The Yukon River–Bering Sea system preserves rare source-to-sink records of these processes across profound changes in global climate during the past 5 million years (Ma). Here, we expand the terrestrial erosion record by dating terraces along the Charley River, Alaska, and explore linkages among previously published Yukon River tributary incision chronologies and Bering Sea sedimentation. Cosmogenic 26Al/10Be isochron burial ages of Charley River terraces match previously documented central Yukon River tributary incision from 2.6 to 1.6 Ma during Pliocene–Pleistocene glacial expansion, and at 1.1 Ma during the 1.2–0.7 Ma Middle Pleistocene climate transition. Bering Sea sediments preserve 2–4-fold rate increases of Yukon River-derived continental detritus, terrestrial and marine organic carbon, and silicate microfossil deposition at 2.6–2.1 and 1.1–0.8 Ma. These tightly coupled records demonstrate elevated terrigenous nutrient and carbon export and concomitant Bering Sea productivity in response to climate-forced Yukon River incision. Carbon burial related to accelerated terrestrial erosion may contribute to CO2 drawdown across the Pliocene–Pleistocene and Middle Pleistocene climate transitions observed in many proxy records worldwide.

Potential for high contribution of urban gardens to nutrient export in urban watersheds

Urban gardens and farms typically use compost as a source of nutrients, often at levels that exceed crop nutrient demands. Although land dedicated to agriculture is a small fraction of urban land use, high input rates coupled with low nutrient use efficiencies suggest that export of nitrogen (N) and phosphorus (P) from this land could be potentially important contributors to urban nutrient budgets. We used the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) Nutrient Delivery Ratio model to examine the potential impact of garden density, compost input rates, and nutrient retention efficiency on N and P export from stormwater runoff for a 737-ha urban residential area in Saint Paul, Minnesota. Although gardens and farms accounted for 0.1-0.5% of land area in our scenarios, compost inputs accounted for as much as 33% of N inputs and 85% of P inputs to the urban landscape. The contribution of gardens to urban nutrient export through stormwater runoff is highly dependent on modeled maximum retention efficiency values. If retention efficiency is high, gardens with low compost inputs are similar to other vegetated land uses in contributions to nutrient export, but gardens become significant contributors to watershed P export if compost inputs are high, or if retention efficiency drops to 75% or lower. These results underscore mass-balance constraints inherent in urban nutrient recycling and highlight the importance of understanding the long-term fate of excess nutrients applied to urban landscapes.