The impact of urbanization on seasonal hydrologic and nutrient budgets of a small North American watershed

Present day hydrologic and nutrient budgets have been measured and presettlement budgets estimated for a small urban watershed in Madison, Wisconsin. The importance of different seasons and sources to the total loading were compared for past and present conditions. The seasonal budget revealed that while spring contributes the greatest loadings in both scenarios, summer exhibits the greatest change in loadings from past to present. As for sources this seepage lake receives most of its water and N from groundwater; however, most P comes from surface runoff. The greatest impact on the watershed since settlement appears to be the large increase in runoff matched by a decrease in evapotranspiration and subsurface flow. This shift in hydrology is largely responsible for the substantial increase in P loading and the decrease in the N : P ratio of total loading. The significance of the lake's modified morphometry to areal and volumetric loading is also explored.     

Nutrient budgets in a dry heathland watershed in northeastern Spain

Dissolved nutrient inputs in bulk precipitation and outputs in streamwater were measured during 3 years of contrasting hydrological conditions in a 6.3-ha, grazed heathland watershed on schists in the Montseny mountains (NE Spain), drained by an intermittent stream. On average, 39% of the precipitation became streamflow. Bulk precipitation delivered positive net alkalinity (mean 0.22 keq/ha/yr), sulphate input was moderate (9.0 kg SO₄-S/ha/yr), and the mean input of inorganic N was not exceptionally high (6.6 kg/ha/yr). Ion concentrations were relatively low in streamwater; SO₄ ^2- was the dominant anion. Most concentrations in streamwater varied seasonally, with maxima in late summer or early autumn and minima in spring. This pattern probably resulted from increased availability of ions for leaching due to decomposition of organic matter and chemical weathering during the warm period. Nitrate concentrations were relatively high in winter and dropped sharply in early spring, probably because of biological uptake. Annual element outputs in streamwater varied between years and seemed to be controlled by both the amount of annual streamflow and its seasonal distribution. Annual inputs exceeded outputs for dissolved inorganic N. The watershed accumulated H⁺ and Ca²⁺, had net losses of Na⁺ and Mg²⁺, and was close to steady state for K⁺, SO₄ ^2-, Cl^- and alkalinity. The chloride budgets gave no evidence of substantial dry deposition in this system. The cationic denudation rate was negative (-0.14 keq/ha/yr) because Ca²⁺ retention was higher than net exports of Na⁺ and Mg²⁺ from silicate weathering. Low nutrient export and little production of alkalinity suggest that this watershed has a low buffering capacity.     

Nutrient uptake in streams draining agricultural catchments of the midwestern United States

1. Agriculture is a major contributor of non‐point source pollution to surface waters in the midwestern United States, resulting in eutrophication of freshwater aquatic ecosystems and development of hypoxia in the Gulf of Mexico. Agriculturally influenced streams are diverse in morphology and have variable nutrient concentrations. Understanding how nutrients are transformed and retained within agricultural streams may aid in mitigating increased nutrient export to downstream ecosystems. 2. We studied six agriculturally influenced streams in Indiana and Michigan to develop a more comprehensive understanding of the factors controlling nutrient retention and export in agricultural streams using nutrient addition and isotopic tracer studies. 3. Metrics of nutrient uptake indicated that nitrate uptake was saturated in these streams whereas ammonium and phosphorus uptake increased with higher concentrations. Phosphorus uptake was likely approaching saturation as evidenced by decreasing uptake velocities with concentration; ammonium uptake velocity also declined with concentration, though not significantly. 4. Higher whole‐stream uptake rates of phosphorus and ammonium were associated with the observed presence of stream autotrophs (e.g. algae and macrophytes). However, there was no significant relationship between measures of nutrient uptake and stream metabolism. Water‐column nutrient concentrations were positively correlated with gross primary production but not community respiration. 5. Overall, nutrient uptake and metabolism were affected by nutrient concentrations in these agriculturally influenced streams. Biological uptake of ammonium and phosphorus was not saturated, although nitrate uptake did appear to be saturated in these ecosystems. Biological activity in agriculturally influenced streams is higher relative to more pristine streams and this increased biological activity likely influences nutrient retention and transport to downstream ecosystems.     

Nitrogen sources and exports in an agricultural watershed in Southeast China

The nitrogen (N) budget was developed for Jiulong River Watershed (JRW), an agricultural watershed in a warm and humid area of southeast China. Water quality monitoring, field surveys, modelling and GIS techniques were applied to estimate N flux of atmospheric deposition, mineralization, runoff, denitrification, and ammonia volatilization. Over the whole watershed, fertilizers, import of animal feeds, biotic fixation, mineralization and atmospheric deposition contributed 67.1%, 16.5%, 2.1%, 4.9% and 9.5%, respectively, of total N input (129.3 kg N ha⁻¹ year⁻¹). Runoff, sale of production, denitrification, and ammonia volatilization contributed 7.3%, 24.4%, 10.5% and 57.8% of total N output (72.9 kg N ha⁻¹ year⁻¹), respectively. The N budget for the JRW suggested that more than 50% of the N input was lost to the environment, and about 14% was discharged as riverine N, which indicated that agricultural and human activities in the watershed substantially impacted the estuary and coastal water quality, and so altered the N biogeochemistry process.     

不同施肥处理对农田生态系统微量元素收支及循环率的影响

以下辽河平原一组长期定位试验为平台,研究了不同施肥制度下农田生态系统微量元素的循环率及当季微量养分收支。结果表明:不同元素在饲喂-堆腐过程中的循环率差异较大,Zn的循环率最低,但也接近80%,Fe、Mn、Cu、Pb的循环率均超过80%,其中Fe、Mn、Pb的循环率均接近90%,微量元素在饲喂-堆腐过程中的循环率随投料量的增加有增加的趋势。以有机肥形式输入农田的微量元素远大于以化肥形式输入农田的量,且输入量随有机肥用量的增加而增加。不同处理间微量元素的移出量以NPK+M处理最高,CK处理最低。各处理土壤微量元素收入小于支出,不同处理间收支差额NPK+M相似文献   

Changes in Production and Nutrient Cycling across a Wetness Gradient within a Floodplain Forest

Floodplain forest ecosystems are highly valuable to society because of their potential for water quality improvement and vegetation productivity, among many other functions. Previous studies have indicated that hydrology influences productivity but that the relationship between hydroperiod and productivity is a complex one. Consequently, we compared multiple indexes of productivity, nutrient circulation, and hydroperiod among three communities on the Flint River floodplain, Georgia, that differed in terms of inundation frequency. We hypothesized that (a) the wettest community would have the lowest total net primary production (NPP) values because of saturated soil conditions; (b) as wetness increases, nutrient circulation in litterfall would decrease because of the hypothesized lower productivity in the wetter community; and (c) as wetness increases, internal translocation would become more efficient. The study site was partitioned into three wetness types—somewhat poorly drained (SPD), intermediate (I) and poorly drained (PD). We found that belowground biomass was greatest on the SPD, litterfall was similar for all three sites, and that woody biomass current annual increment (CAI) was greatest in the PD community. However, when the three variables were totaled for each site, the PD had the greatest NPP, thus disproving hypothesis (a). For hypothesis (b), we observed that P content in litterfall, although not significant, followed the predicted trend; nitrogen (N) content displayed the opposite pattern (PD > I > SPD). As wetness increased, internal translocation became more efficient for phosphorus (support for hypothesis [c]), but the SPD community was more efficient at retranslocating N (contradiction of hypothesis [c]). Received 19 June 2000; accepted 19 October 2000.     

An Exotic Tree Alters Decomposition and Nutrient Cycling in A Hawaiian Montane Forest

We evaluated the effects of the exotic tree Fraxinus uhdei on decomposition dynamics and nutrient turnover in a montane Hawaiian rainforest. We used reciprocal transplants of litterbags between forests dominated by Fraxinus and by the native Metrosideros polymorpha to distinguish between endogenous (litter quality) and exogenous (for example, microclimate, nutrient availability, microbial and invertebrate communities) effects of Fraxinus on mass loss and nutrient dynamics of decomposing litter. Fraxinus produced greater quantities of litter that was thinner, had higher N and P concentrations, and lower concentrations of lignin and soluble polyphenols. Microbes decomposing Fraxinus litter produced fewer enzymes involved in N and P acquisition and more of those involved in cellulose degradation. Differences in litter quality and microbial activity resulted in a strong effect of litter type on rates of mass loss, whereby Fraxinus litter decomposed and released nutrients at nearly twice the rate of Metrosideros litter (k=0.82 versus 0.48), regardless of site of decomposition. Although site of decomposition had no effect on rates of litter mass loss, Fraxinus litter decomposed under a Fraxinus canopy mineralized approximately 20% less P after one year than Fraxinus litter decomposed under a Metrosideros canopy. Furthermore, Fraxinus litter decomposed under a Fraxinus canopy immobilized greater amounts of N and P in the early stages of decay, suggesting that the large amounts of N and P in Fraxinus litterfall have raised nutrient availability to decomposers in the forest floor. Greater immobilization of N and P under a Fraxinus canopy may act as a governor on rates of nutrient cycling, limiting the degree to which Fraxinus invasion accelerates N and P cycling in this system.     

Nutrient cycling in Pinus sylvestris stands in eastern Finland

Nutrient cycling within three Pinus sylvestris stands was studied in eastern Finland. The aim of the study was to determine annual fluxes and distribution of N, P, K, Ca, Mg, Zn, Fe, B, and Al in the research stands. Special emphasis was put on determining the importance of different fluxes, especially the internal cycle within the trees in satisfying the tree nutrient requirements for biomass production. The following nutrient fluxes were included, input; free precipitation and throughfall, output; percolation through soil profile, biological cycle; nutrient uptake from soil, retranslocation within trees, return to soil in litterfall, release by litter decomposition. The distribution of nutrients was determined in above- and belowground tree compartments, in ground and field vegetation, and in soil.The nitrogen use efficiencies were 181, 211 and 191 g of tree aboveground dry matter produced per g of N supplied by uptake and retranslocation in the sapling, pole stage and mature stands, respectively. Field vegetation was more efficient in nitrogen use than trees. Stand belowground/aboveground and fine root/coarse root biomass ratios decreased with tree age. With only slightly higher fine root biomass, almost three times more nitrogen had to be taken-up from soil for biomass production in the mature stand than in the sapling stand.The annual input-output balances of most nutrients were positive; throughfall contained more nutrients than was lost in mineral soil leachate. The sulphate flux contributed to the leaching of cations, especially magnesium, from soil in the mature stand.Retranslocation supplied 17–42% of the annual N, P and K requirements for tree aboveground biomass production. Precipitation and throughfall were important in transferring K and Mg, and also N in the sapling stand. Litterfall was an important pathway for N, Ca, Mg and micro nutrients, especially in the oldest stands.     

The nutrient budgets of a watershed and its forest ecosystem in the Taï National Park in Cô d'Ivoire

Atmospheric inputs and stream water outputs of P, K,Ca and Mg were estimated for an undisturbed forestedwatershed and the forest ecosystem within it inTaï National Park, Côte d'Ivoire in 1990/91.The study included measurements of wet and drydeposition, and suspended sediments, organic debrisand solutes in the water flows. Base flow as well asquick flow were sampled. The nutrient budgets of theentire watershed and the forest ecosystem (comprisingvegetation and rooted soil layers) were distinguishedon the basis of two assumptions (i) solutes in thebase flow are derived from the soil layers below therooted zone only, and hence not from the forestecosystem; (ii) the total soil mass in the rooted zoneremains constant, i.e. the export of topsoil materialby erosion is compensated for by deepening the rootzone. The first assumption was supported by theresemblance of the molar ratios of solutes in the baseflow and those calculated for the weathering of themigmatite found in the soil layers below the rootedzone. It is concluded that the stocks of P, K, Caand Mg in the watershed are decreasing with 1.4, 12.7,15.3, and 8.1 kg ha^-1 yr^-1 respectively.Losses are mainly a result of nutrient exports byerosion and solutes in the base flow. Nutrient stocksfor the forest ecosystem are also apparentlydecreasing, but to a much lesser extent, indicatingthe importance of distinguishing between the watershedand the forest ecosystem within.     

Foliar and Litter Nutrients, Nutrient Resorption, and Decomposition in Hawaiian Me t rosideros polymorpha

The native tree Metrosideros polymorpha dominates Hawaiian forests across a very wide range of soil fertility, including both sites where forest production is limited by nitrogen (N) and others where it is limited by phosphorus (P). Five long-term fertilization experiments have further broadened the range of nutrient availabilities experienced by Metrosideros. Adding P to P-limited sites increased foliar P concentrations threefold and litter P concentrations up to 10-fold; lignin concentrations decreased, and the decomposability of leaf litter increased from 32%–35% to 36%–46% mass loss in the first year. Adding N to N-limited sites increased leaf and litter N concentrations by only 15%–20%, with little or no effect on the decomposability of tissue. Received 22 January 1998; accepted 4 May 1998.     

土壤—作物系统的养分转化及其对土壤养分平衡的影响

土壤作为一个开放系统,与作物间通过物质转化与能量流动组成相互依存和影响的体系。近几年来我们对我国太湖地区稻田土壤生态系统中氮、磷、钾养分的转化及其可能产生的影响作过为期3年的田间定位试验研究,本文谨将其中的部分结果整理成文,以供共同探讨。     

Gaseous nitrogen emmissions from undisturbed terrestrial ecosystems: An assessment of their impacts on local and global nitrogen budgets

There is increasing interest in the importance of nitrogen gas emissions from natural (non-agricultural) ecosystems with respect to local as well as global nitrogen budgets and with respect to the effects of nitrogen oxides on atmospheric ozone levels and global warming. The volatile forms of nitrogen of common interest are ammonia (NH₃), nitrous oxide, (N₂O), dinitrogen (N₂), and NO_x (principally NO + NO₂). It is often difficult to attribute emissions of these compounds from soils to a single process because they are produced by a variety of common biogeochemical mechanisms. Although environmental conditions in the soil often appear to favor nitrogen gas emissions, the potential nitrogen gas emission rate from undisturbed ecosystems is rarely approached. The best estimates to date suggest that nitrogen gas emission rates from undisturbed ecosystems typically range from > 1 to perhaps 10 or 20 kg N ha^-1 yr^-1. Under certain conditions, however, emission rates may be much higher. For example, excreta from animals in grasslands may elevate ammonia volatilization up to 100 kg N ha^-1 yr^-1 depending on grazer density; tidal input of nutrients to coastal wetlands may support denitrification rates of several hundred kg N ha^-1 yr^-1 . Excepting such cases, gaseous nitrogen losses are probably a small component of the local nitrogen budget in most undisturbed ecosystems. However, emissions from undisturbed soils are an important component of the global source strengths for (N₂O + N₂), N₂O and NO_x (50%, 21%, and 10% respectively). Emission rates of N₂O from natural ecosystems are higher than assumed previously by perhaps 10 times. Large-scale disturbance may have a stimulatory effect on nitrogen emission rates which could have important effects on global nitrogen budgets. There is a need for more sophisticated methods to account for natural temporal and spatial variations of emissions rates, to more accurately and precisely assess their global source strengths.     

Water budgets and nutrients in a native Banksia woodland and an adjacent Medicago sativa pasture

In southern Australia, the spread of dryland salinity can be traced to increased leakage of water through the root zone to the groundwater, associated with clearing of perennial vegetation and its replacement with annual crops and pastures. Agricultural activity, through fertilizer addition and subsequent nutrient export, has also changed the nutrient status of the soils, often causing increases in soil acidity. In this trial, an area of native vegetation on a deep sandy soil in south-western Australia (dominated by Banksia prionotes Lindley), and an adjacent introduced perennial pasture (Medicago sativa L.), were compared in terms of their water balance and nutrient fluxes for the period between August 1998 and March 2001. Initially, the Banksia woodland vegetation maintained a drier soil profile below 2 m than the establishing lucerne pasture, and leakage beyond 4 m in 1999 was 80 mm under the Banksia woodland and 180 mm under the lucerne. However, in 2000, lucerne's rate of water use during winter was faster than any other vegetation observed on this soil type, possibly due to direct groundwater extraction, and it dried the soil to the same level as the Banksia woodland vegetation. Nutrient (nitrate, phosphate, sulphate, potassium, calcium, magnesium and sodium) fluxes under both systems were generally low, reflecting the inherently low fertility of the soil type. However, sodium and nitrate appeared to accumulate in soil at a depth of 4 m under the Banksia woodland (particularly between the Banksia canopies), but not under the lucerne, possibly due to a history of leaching under the lucerne. Whilst both vegetation types effectively controlled excess water leakage, the differences in nutrient cycling and production levels suggests that some aspects of native perennial vegetation function may not be suitable for incorporation into agricultural systems.     

The effects of quantity and duration of simulated pollutant nitrogen deposition on root-surface phosphatase activities in calcareous and acid grasslands: a bioassay approach

A field and laboratory based bioassay has been developed to investigate the effects of the quantity and duration of simulated pollutant nitrogen (N) deposition on root-surface phosphomonoesterase (PME) activities in calcareous and acid grasslands. Seedlings of Plantago lanceolata were transplanted to a calcareous grassland and Agrostis capillaris seedlings were grown in microcosms containing soil from an acid grassland that had received either 7 yr (long-term) N additions or 18 months (short-term) N and phosphorus (P) additions. The bioassay revealed that short-term N treatments had little effect on the enzyme activity, whereas long-term N additions significantly increased PME activity within 7 d of transplanting into the field plots. Root-surface PME activity of A. capillaris was significantly reduced in soil that received additions of P. In the plots receiving long-term additions of N, a strong relationship was observed between extractable soil ammonium and root-surface PME activity. Soil ammonium concentrations accounted for 67% of the variation in PME activity of P. lanceolata in the calcareous grassland, and 86% of the variation in PME activity of A. capillaris in the acid grassland. These results provide evidence that N deposition may have considerable effects on the demand and turnover of P in ecosystems that are approaching or have reached N saturation.     

Soil nutrient budgets following projected corn stover harvest for biofuel production in the conterminous United States

Increasing demand for food and biofuel feedstocks may substantially affect soil nutrient budgets, especially in the United States where there is great potential for corn (Zea mays L) stover as a biofuel feedstock. This study was designed to evaluate impacts of projected stover harvest scenarios on budgets of soil nitrogen (N), phosphorus (P), and potassium (K) currently and in the future across the conterminous United States. The required and removed N, P, and K amounts under each scenario were estimated on the basis of both their average contents in grain and stover and from an empirical model. Our analyses indicate a small depletion of soil N (?4 ± 35 kg ha^?1) and K (?6 ± 36 kg ha^?1) and a moderate surplus of P (37 ± 21 kg ha^?1) currently on the national average, but with a noticeable variation from state to state. After harvesting both grain and projected stover, the deficits of soil N, P, and K were estimated at 114–127, 26–27, and 36–53 kg ha^?1 yr^?1, respectively, in 2006–2010; 131–173, 29–32, and 41–96 kg ha^?1 yr^?1, respectively, in 2020; and 161–207, 35–39, and 51–111 kg ha^?1 yr^?1, respectively, in 2050. This study indicates that the harvestable stover amount derived from the minimum stover requirement for maintaining soil organic carbon level scenarios under current fertilization rates can be sustainable for soil nutrient supply and corn production at present, but the deficit of P and K at the national scale would become larger in the future.     

Nutrient recycling by fish in streams along a gradient of agricultural land use

Nutrient recycling is an essential ecosystem process provided by animals. In many aquatic systems, fish have been identified as important in ecosystem nutrient recycling; however, this importance can vary widely between systems. The factors controlling intersystem variation in animal‐mediated nutrient cycling have rarely been examined and as such it remains unclear what impact human landscape changes will have upon these processes. Here we examined rates of nutrient recycling for temperate stream fish assemblages along a gradient of agricultural land use (proportion cropland in the watershed: 1–59%). We quantified nutrient excretion rates of both ammonium–N (NH₄⁺–N) and phosphate (as soluble reactive phosphate: SRP) for fish assemblages at eight streams in southern Ontario, Canada with species‐specific excretion measurements and quantitative assemblage sampling. For both nutrients, total assemblage excretion exhibited a strong positive relationship with riparian cropland. The distance required for fish assemblages to turn over ambient nutrient pools was shorter for cropland systems, indicating that the relative importance of excreted nutrients was higher in these systems. Based on measured uptake rates of NH₄⁺–N in two streams (one higher cropland and one low cropland) and on modeled uptake rates for all streams, the proportion of ecosystem demand that can be satisfied by excretion is generally higher in the more agricultural streams. These patterns appear to be driven largely by disproportionate increases in fish assemblage biomass with increasing stream nutrient concentrations.     

Nitrogen budget and gaseous nitrogen loss in a tropical agricultural watershed

Although agricultural systems in tropical monsoon Asia play a central role in the global nitrogen (N) cycle, details of the N cycle in this region on a watershed scale remain unclear. This study quantified the N budget in a tropical watershed of 221 km² on Java Island, where paddy fields cover 28% of the land, by conducting field surveys. The amount of net biochemical gaseous N loss to the atmosphere (X _GB ), which is generally difficult to determine, was calculated as the residual of the N balance. Assuming that NH₃ volatilization balances deposition, and hence subtracting NH₄–N from the N import with atmospheric deposition, the average total import and export of N per year was found to be 46.5 kg ha⁻¹ year⁻¹ over the watershed. Of this, 71% was imported as fertilizer (M _F ) and 29% with atmospheric deposition (M _AD ). On the export side, 42% was lost as X _GB , 37% with incineration of rice residues and wood fuel (X _GI ), 13% with river discharge (X _D ) and 9% with rice surplus export (X _R ). A large portion of X _GB , and consequently, a small portion of X _D could be explained by the high rate of denitrification resulting from the high temperature and humid climate, and are thought to be common features of tropical watersheds where paddy fields are found.