Explore the vast range of titles available.

In order to assess the progress toward eutrophication management goals, it is important to understand trends in land-based nutrient use. Here we present net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) for 2000 and 2010 for the Baltic Sea watershed. Overall, across the entire Baltic, between the 5-year periods centered on 2000 and 2010, NANI and NAPI decreased modestly by –6 and –4%, respectively, but with substantial regional variation, including major increases in the Gulf of Riga drainage basin (+19 and +58%, respectively) and decreases in the Danish Straits drainage basin (–25 and –40% respectively). The changes were due primarily to changes in mineral fertilizer use. Mineral fertilizers dominated inputs, at 57% of both NANI and NAPI in 2000, increasing to 68 and 70%, respectively, by 2010. Net food and feed imports declined over that period, corresponding to increased crop production; either fewer imports of food and feedstocks were required to feed humans and livestock, or more of these commodities were exported. A strong linear relationship exists between regional net nutrient inputs and riverine nutrient fluxes for both periods. About 17% of NANI and 4.7% of NAPI were exported to the sea in 2000; these relationships did not significantly differ from those for 2010. Changes in NANI from 2000 to 2010 across basins were directly proportional rather than linearly related to changes in total N (TN) fluxes to the sea (i.e., no change in NANI suggests no change in TN flux). Similarly, for all basins except those draining to the Baltic Proper, changes in NAPI were proportional to changes in total P (TP) fluxes. The Danish Straits decreased most between 2000 and 2010, where NANI and NAPI declined by 25 and 40%, respectively, and corresponding fluxes of TN and TP declined 31 and 18%, respectively. For the Baltic Proper, NAPI was relatively unchanged between 2000 and 2010, while riverine TP fluxes decreased 25%, due possibly to lagged effects of fertilizer reduction resulting from socio-political changes in the early 1990s or improvements in sewage treatment capabilities. For most regions, further reductions in NANI and NAPI could be achieved by more efficient production and greater substitution of manure for imported mineral fertilizers.

Intense human activities have increasingly reshaped the global nutrient cycle, causing frequent environmental issues owing to excessive nitrogen (N) and phosphorus (P) inputs. Therefore, it is necessary to explore the component structure, driving factors, and environmental impacts of regional nutrient inputs. Based on net anthropogenic N and P input (NANI and NAPI, respectively) models, combined with data mining and statistical analysis, the spatiotemporal changes of NANI and NAPI in the Yangtze River Basin were studied. Their environmental and scale effects, policy impacts, and classification management were then discussed. The results reveal that NANI and NAPI showed a significant downward trend in the Yangtze River Basin from 2011 to 2019, with an average value of 7968 kg N km−2 year−1 and 1241 kg P km−2 year−1, respectively. Moreover, the contribution of varying fertilizer intensity resulted in an approximate change in both NANI and NAPI by 50%. Meanwhile, NANI and NAPI exhibited decreasing spatial trends from east to west and north to south, with developed agricultural plain areas and densely populated urban agglomeration areas being the focal areas of nutrient inputs. Despite the spatiotemporal differences, there was a strong dependence between higher nutrient input and higher nutrient concentration conditions. To relieve the environmental pressure, the fertilizer policy was implemented and had a marked impact on the change in nutrient input trend. Based on the classification of cities through the comparison of major input items, plain regions where fertilizer dominates nutrient input need to be managed by improving the utilization rate of fertilizer.

Terrestrial-based nutrient pollution has emerged as one of the most detrimental factors to coral health in many reef habitats. Recent studies have shown that excessive dissolved inorganic nutrients can reduce coral thermal tolerance thresholds and even exacerbate bleaching during thermal stress, yet the effects of minor nutrient enrichment under heat stress have not been extensively studied. In this study, Lobactis scutaria , Montipora capitata , and Pocillopora acuta colonies under heated conditions (~30.5 °C) were exposed to low and balanced nitrogen and phosphorous concentrations over a 31-day heating period. Coral colonies were collected from Kāne‘ohe Bay, O‘ahu, which has a unique history of nutrient pollution, and held in mesocosms that allowed for environmental manipulation yet are also influenced by local field conditions. Principal findings included delays in the bleaching of nutrient-enriched heated colonies as compared to heated-only colonies, in addition to relatively greater calcification rates and lower proportions of early-stage paling. Species-specific outcomes were prevalent, with L. scutaria demonstrating no difference in calcification with enrichment under heat stress. By the end of the heating stage, however, many heated colonies were at least partially impacted by bleaching or mortality. Despite this, our findings suggest that low levels of balanced nutrient enrichment may serve as a mitigative force during thermal events. Further field-based studies will be required to assess these results in different reef habitats.

Total organic carbon (TOC), total nitrogen (TN), stable carbon and nitrogen isotopes (δ 13 C, δ 15 N), total phosphorus (TP) and organic phosphorus (OP) were measured in surface sediments and two short cores (DU-3 and WS-4) from Lake Nansihu, China to infer historical changes in anthropogenic nutrient inputs and corresponding shifts in lake primary productivity. Results indicate that organic matter preserved in the sediments is mainly autochthonous and that analyzed sediment variables were affected little by post-burial diagenesis. Increasing TOC, TN, OP and TP concentrations since the 1940s reflect increased P loading and elevated lake productivity. The δ 13 C values varied from −21.5 to −26.6‰ in the two sediment cores. Values were relatively more negative before the 1940s, but thereafter increased until the mid-1980s, reflecting elevated lake productivity. Since the mid-1980s, δ 13 C values remained relatively constant in core WS-4 and decreased in core DU-3, perhaps reflecting a change in the phytoplankton community. The δ 15 N values ranged from −0.5 to 1.3‰ in core DU-3 and from 1.2 to 2.5‰ in core WS-4 before the mid-1980s, and increased to between 2.1 and 8.0‰ and 5.2 and 7.8‰, respectively, thereafter. Topmost sediments in the two cores display δ 15 N values similar to those recorded in the surface sediments (5.5–7.5‰). Higher δ 15 N values in recent deposits correspond to greater nitrogen concentration in water, and likely indicate anthropogenic nitrogen input, mainly from human and animal wastes.

This chapter contains sections titled: References

Given the regulatory impact of resources and consumers on plant production, decomposition, and soil carbon sequestration, anthropogenic changes to nutrient inputs and grazing have likely transformed how grasslands process atmospheric CO 2 . The direction and magnitude of these changes, however, remain unclear in this system, whose soils contain ∼20% of the world's carbon pool. Nutrients stimulate production but can also increase tissue palatability and decomposition. Grazing variously affects tissue quality and quantity, decreasing standing biomass, but potentially increasing leaf nutrient concentrations, root production, or investment in tissue defenses that slow litter decay. Here, we quantified individual and interactive impacts of nutrient addition and simulated grazing (mowing) on above- and belowground production, tissue quality, and soil carbon inputs in a western North American grassland with globally distributed agronomic species. Given that nutrients and grazing are often connected with increased root production and higher foliar tissue quality, we hypothesized that these treatments would combine to reduce inputs of recalcitrant-rich litter critical for C storage. This hypothesis was unsupported. Nutrients and defoliation combined to significantly increase belowground production but did not affect root tissue quality. There were no significant interactions between nutrients and defoliation for any measured response. Three years of nutrient addition increased root and shoot biomass by 37% and 23%, respectively, and had no impact on decomposition, resulting in a ∼15% increase in soil organic matter and soil carbon. Defoliation triggered a significant burst of short-lived lignin-rich roots, presumably a compensatory response to foliar loss, which increased root litter inputs by 33%. The majority of root and shoot responses were positively correlated, with aboveground biomass a reasonable proxy for whole plant responses. The exceptions were decomposition, with roots six times more decay resistant, and grazing impacts on tissue chemistry, with shoots undergoing significant alterations, while roots were unaffected. Because neither treatment affected concentrations of decay-resistant compounds in roots, the implied net effect is higher soil C inputs with potentially longer residency times. Areas managed with nutrients and moderate grazing in our study system could thus accumulate significantly more soil C than unmanaged areas, with a greater capacity to serve as sinks for atmospheric CO 2 .

Rainfall is one of the primary sources of chemical inputs in forest ecosystems, and the basis of forest nutrient cycling. Mixed evergreen and deciduous broadleaved forests are currently one of the most threatened ecosystems due to their sensitivity to anthropogenic climate change. As such, understanding the hydrochemical fluxes of these systems is critical for managing their dynamics in the future. We investigate the chemistry of bulk precipitation, stemflow and throughfall in a mixed evergreen and deciduous broadleaved forest in the Shennongjia region of Central China. Mean nutrient concentrations in throughfall and stemflow were higher than in bulk precipitation. Stemflow ion fluxes from deciduous tree species were greater than those for evergreen tree species because of the differences in bark morphology and branch architecture. Throughfall and stemflow chemistry fluctuated dramatically over the growing season. Nitrate nitrogen and ammonium nitrogen were retained, while other elements and compounds were washed off or leached via throughfall and stemflow pathways. Our findings will facilitate a greater understanding of nutrient balance in canopy water fluxes.

Coastal lagoons are important for ecological, cultural, economic and recreational reasons. Globally, they are subject to significant anthropogenic pressures. Our understanding of the importance of groundwater discharge into coastal lagoons for water and solute budgets is evolving, yet key gaps remain. This study resolves sources of groundwater seepage and estimates nutrient loads from direct groundwater discharge into a large hypertrophic coastal lagoon in New Zealand. We analysed major ions, stable water isotopes and nutrients in lagoon surface water, porewater, groundwater wells and springs. Groundwater and porewater samples split into two distinct groups: (1) inland samples that were MgHCO3 dominated with more negative δ2H:δ18O ratios and lower ion concentrations, and (2) permeable barrier samples that were NaCl dominated with more positive δ2H:δ18O ratios and higher ion concentrations. Porewater entering the lagoon is sourced from alpine river and rainfall recharge on the plains. Barrier porewater appears to be sourced from infiltration from the lagoon through the barrier and local rainfall. Despite higher nitrate in deeper groundwater wells, low nitrate in shallow porewater indicates potential denitrification before groundwater discharges to the lagoon. Our observations support efforts to restore and construct wetlands around the lagoon to remove nutrients. However, wetland restoration will need to be carried out by maintaining a balance between enhancing denitrifying conditions while preventing phosphorus release from sediments. Nutrient load calculations revealed that direct groundwater seepage to the lagoon provides ~ 3% of dissolved inorganic nitrogen and ~ 30% of dissolved reactive phosphorus compared to river inputs, indicating that groundwater discharge may play an important role in phosphorus transport to the lagoon.

Cold-temperate headwaters of Patagonia are interdigitated in a narrow sector of the Andes mountains devoid of anthropogenic impacts and thus are suitable systems to evaluate the climate and landscape controls on terrestrial-aquatic fluxes. In this investigation we focused on evaluating dissolved organic matter (DOM) and nutrient dynamics in a stream born in a mountain lake draining a steep forested catchment, a typical configuration of Andean-Patagonian headwaters. Stream water chemistry was studied throughout the hydrologic year and at different sites along the altitudinal drainage gradient. The analyses showed extremely low nutrient and dissolved organic carbon (DOC) concentrations and low primary production within the ranges of ultraoligotrophy. Pulses of terrestrial DOM and nutrient inputs were detected during rainfall events and in snowmelt periods, shifting distinctively the nutrients as well as the DOC concentration and quality from baseflow conditions. Stream DOM pools, characterized through optical methods, showed the prevalence of terrigenous humic components (C1 and C2) and a small contribution of a non-humic component (C3), with rainfall runoff increasing the C2 and snowfall enhancing the C3. Stream sites at higher elevation were influenced by the upstream lake showing signatures of phytoplankton production and degradation in their DOM pools, whereas downstream points displayed higher terrestrial prints.The results presented here contribute to understanding carbon and nutrient dynamics in cold-temperate pristine freshwaters of the Southern Hemisphere, which are underrepresented in global studies and differ substantially from temperate systems of the Northern Hemisphere in terms of climate and anthropogenic pressures.

We provide data on nutrient export for 28 rivers in southwestern Europe and analyze long-term changes in the context of anthropogenic pressures and regulation policies. Special attention is given to seasonal variations, because the integrated annual values that are usually provided do not allow us to establish comparisons with seasonal phytoplankton dynamics. The eutrophication risk associated with river inputs is addressed by means of an indicator (Index of Coastal Eutrophication Potential, ICEP, Billen and Garnier, Mar Chem 106:148–160, 2007). An overview of the temporal evolution and the intra-annual variability of the ICEP is discussed for specific rivers and integrated coastal regions. The annual dynamics of the eutrophication indicator is analyzed to delimit those periods when the risk of eutrophication is particularly high. The trends in nutrient fluxes and coastal phytoplankton are compared by means of a case study (Seine Bay). The decrease in phosphorus matches a general decrease in phytoplankton biomass in the summer. However, sustained high values of nitrogen still foster the emergence of harmful algal blooms, and we found an increase in the summer abundance of dinoflagellates. The abatement of phosphorus alone is not enough to shortcut harmful blooms and toxic outbreaks in the Seine Bay. A reduction in nitrogen inputs may be necessary to effectively minimize eutrophication problems.