Spatiotemporal modeling of watershed nutrient transport dynamics: Implications for eutrophication abatement

The main objective of this study was to quantify nutrient transport dynamics of a previously ungauged, temperate watershed (145 km²) surrounding a shallow eutrophic lake and discern lake response to external nutrient loading, based on soil water assessment tool (SWAT) and the Organization of Economic Cooperation and Development (OECD) empirical lake models, respectively. A SWAT model was used to simulate baseline nutrient dynamics after its calibration and validation against daily tributary flow, total dissolved phosphorus (TDP), total phosphorus (TP), and nitrate (NO₃) loads. On the watershed scale, median annual TDP, TP, and NO₃ losses were 0.4, 1.1, and 2.0 kg ha^− 1, respectively. The highest median annual TP and NO₃ losses were estimated at 3.7 and 7.7 kg ha^− 1 for pastureland and 1.7 and 3.8 kg ha^− 1 for cropland and mixed forests, respectively. Baseflow was the major nutrient transport pathway over a wide range of precipitation events (450 to 900 mm yr^− 1). Erosion was the predominant surface process exporting P across the watershed. Critical source areas (CSAs) of TP and NO₃ comprised 17% and 4% of the watershed, respectively. Annual mean TP, and mean and maximum chlorophyll content indicated a hyper-eutrophication risk for the lake. An external P load reduction by excess of 80% could be necessary to restore mesotrophy in the lake. Our results suggested that subsurface P transport should not be overlooked a priori when groundwater-dependent and extensively farmed watersheds are managed for eutrophication abatement.     

生态安全条件下土地利用格局优化——以皇甫川流域为例

在人类活动导致的生态环境问题中,土地利用格局变化对区域生态安全起着决定性作用。选择我国乃至在世界上都罕见的多沙、粗沙、强烈水土流失的黄河皇甫川流域作为研究区域,针对土壤侵蚀和生态用水这两大影响流域生态安全的关键问题,开展土地利用变化模拟、土壤侵蚀3S监测、适宜植被盖度估算、土壤侵蚀情景模拟、土地利用格局优化等方面的综合研究。结果表明:(1)土地利用格局变化是导致土壤侵蚀变化的重要因素。从1987年到2015年,建筑用地、林地和灌丛面积增加,水域、沙地和裸砒砂岩面积减少,导致流域年平均土壤侵蚀模数由16160.72 t km-2a-1降至9710.72 t km-2a-1。(2)土地利用类型与土壤侵蚀模数密切相关并存在一定规律。6种不同土地利用类型多年平均土壤侵蚀模数的大小顺序为:裸砒砂岩沙地耕地草地林地灌丛,表明灌、林措施是流域植被恢复和土壤侵蚀减少的首选。(3)土地利用结构和空间格局优化有助于提升区域生态安全水平。在优化格局下,2007年和2015年土壤侵蚀模数比优化前分别减少5469.57 t km-2a-1和5432.77 t km-2a-1,优化后2015年土壤侵蚀模数仅为4277.95 t km-2a-1,低于流域自然侵蚀临界值或允许土壤侵蚀模数5300 t km-2a-1,优化土地利用格局成为加强流域生态环境建设的重要途径。     

Simulation of land use–soil interactive effects on water and sediment yields at watershed scale

Influences of vegetation management on soil erosion have been extensively studied. However, interactive effects between land use and soil are poorly documented in literature. Given the importance of understanding such effects for successful watershed management, the objective of this study was to examine the land use–soil interactive effects on water and sediment yields for the 117,845-ha drainage area upstream of the U.S. Geological Survey flow gauging station 08101000 in the Cowhouse Creek watershed located in north central Texas. The examination was implemented using the Soil and Water Assessment Tool (SWAT), a distributed watershed model that has been widely used to tackle problems relevant to nonpoint source pollution. A SWAT model was calibrated and validated in accordance with the observed daily streamflows at this gauging station. Subsequently, the calibrated model was used to examine changes of water and sediment yields as a result of the conversion of range brush to range grasses on an individual soil basis. The results indicated that for the study area, the removal of range brush would result in an annual water yield increase of 24 mm ha^?1 treated area. However, the removal on an upland soil with a moderately high permeability was predicted to increase the annual water yield by 80 mm ha^?1 treated area, while it would result in a small increase of annual sediment loading (4.2 t ha^?1 treated area) and a minimal alteration to the existing spatial patterns of sediment sources. The increase of water yield would be larger for the removal of range brush on a soil that is adjacent to the stream channels. For a given soil, the predicted water yield increase was greater for the wetter hydrologic condition than that for the drier one. A reasonable generalization of this study was that the development of best management practices for watershed health and sustainability may need to take into account land use–soil interactive effects on an individual soil basis.     

In situ and satellite observations of a harmful algal bloom and water condition at the Pearl River estuary in late autumn 1998

Harmful algal blooms (HABs) have posed a serious threat to the aquaculture and fisheries industries in recent years, especially in Asia. During 1998 there were several particularly serious blooms in the coastal waters of south China, which caused a serious damage to aquaculture. We report a massive dinoflagellate bloom near the mouth of Pearl River in November 1998 with analyses of data from both in situ sea water measurements and satellites. A multi-parameter environmental mapping system was used to obtain real-time measurements of water quality properties and wind data through the algal bloom area, which allow us to compare water measurements from inside and outside of the bloom areas. This bloom with high concentrations of algal cells was evident as a series of red colored parallel bands of surface water that were 100–300 m long and 10–30 m wide with a total area of about 20–30 km² by visual. The algal density reached 3.8×10⁷ cells l⁻¹ and the surface chlorophyll-a (Chl-a) concentration was high. The algal species has been identified as Gymnodinium cf. catenatum Graham. The water column in the bloom area was stratified, where the surface temperature was 24–25 °C, the salinity was 18–20%, and the northern wind was about 3–4 m s⁻¹ in the bloom area. The SeaWiFS image has shown high Chl-a area coinciding with the bloom area. The sea surface temperature (SST) image of the Pearl River estuary combined with the in situ measurements indicated that the bloom occurred along a mixing front between cooler lower salinity river water and warmer higher saline South China Sea (SCS) water.     

Quantification and assessment of changes in ecosystem service in the Three-River Headwaters Region,China as a result of climate variability and land cover change

Rapid and periodic assessment of the impact of land cover change and climate variability on ecosystem services at regional levels is essential to understanding services and sustainability of ecosystems. This study focused on quantifying and assessing the changes in multiple ecosystem services in the Three-River Headwaters Region (TRHR), China in 2000–2012. Based on the widely used biophysical models including Integrated Valuation of Ecosystem Services and Trade-Offs (InVEST), Revised Wind Erosion Equation (RWSQ), and Carnegie-Ames-Stanford Approach (CASA) models, this study assessed the historical flow of regulating services, including soil conservation, water yield, and carbon sequestration, and provisioning service food provision. The soil conservation function of ecosystem was slightly enhanced as a whole, and water yield increased sharply, with both the soil conservation and water yield showing an increasing spatial homogenization. The net primary productivity (NPP) and food production increased substantially from 2000 to 2012. Ecosystem services are closely and complexly interlinked. The correlation analyses indicated a trade-off between the water yield and carbon sequestration, however, a synergy between soil conservation and carbon sequestration. Congruence between the three different ecosystem provisioning services, including pasture, meat, and grain, was found. There was also a synergy between food production and ecosystem carbon sequestration in the TRHR. Climatic variability and vegetation restoration are important for the ecosystem services flow. Correlation analyses showed that the increase in precipitation significantly enhanced the water yield (P < 0.01) and soil erosion (P < 0.01), while the temperature increase influenced positively the NPP (P < 0.1). The experience of ecological rehabilitation and the change in key ecosystem services in the TRHR exemplified the positive effects of environmental policies and the necessity of adopting an adaptive management approach. Thus the ecological construction and policy making should take climate variability into account, and facilitate synergies on multiple ecosystem services in order to maximize human well-being and preserve its natural ecosystems.     

Long-term trend of Ulva prolifera blooms in the western Yellow Sea

Blooms of the green macroalga Ulva prolifera in the western Yellow Sea occurred every year since 2008, and they have been reported and studied extensively using a variety of means including remote sensing. However, to date, long-term bloom patterns have not been reported except for a few case studies showing examples in different years. Here, using MODIS observations and an objective method to perform statistical analysis, mean Ulva coverage in the western Yellow Sea has been derived and analyzed between 2007 and 2015 at both monthly and annual scales. On annual scale, mean Ulva coverage decreased after 2008, but increased rapidly after 2012 from 8 km² in 2012 to 116 km² in 2015 (the largest ever reported in history for this region). In the month of June the mean coverage increased from 18 km² in 2012 to 363 km² in 2015. Other than 2009 and 2010, the month of June showed maximum Ulva coverage in every year. These coverage estimates are significantly lower than previously reported values as they represent “pure” algae coverage after taking into account of partial pixel coverage. Several environmental factors were examined in an attempt to determine the reasons behind such long-term changes, yet the results are inconclusive, suggesting a strong necessity of further coordinated and multi-disciplinary researches.     

黄河流域生态安全屏障防风固沙时空变化及驱动因素

黄河流域是我国重要的生态屏障和经济区,防风固沙服务及其驱动机制的研究对于筑牢黄河流域生态安全屏障具有重要意义。基于修正土壤风蚀模型(RWEQ)定量评估黄河流域2000—2018年防风固沙服务时空变化,采用相关分析和地理加权回归模型(GWR)从社会、气候、土壤、植被、地形等角度探究各驱动因素对黄河流域防风固沙服务影响的空间异质性。结果表明：(1)2000—2018年黄河流域土壤风蚀模数与单位面积防风固沙量分别以0.04 t hm^-2 a^-1和0.14 t hm^-2 a^-1的速率下降,而防风固沙保有率和植被覆盖度则分别以0.05%·a^-1和0.26%·a^-1的速率上升。(2)黄河流域土壤风蚀以微度(<2 t hm^-2 a^-1)和轻度(2—25 t hm^-2 a^-1)为主,共占研究区面积的96.28%。土壤风蚀在空间分布呈现西北高东南低的特点,而防风固沙服务高值则主要分...     

Forest degradation assessment in the upper catchment of the river Tons using remote sensing and GIS

The present study investigates the status of forest degradation in the upper catchment of the river Tons in the Uttarakhand state of India, including Govind Wildlife Sanctuary and the National Park by the same name using remote sensing and the geographic information system (GIS). The study revealed that more than 50% of the study area is covered with snow and the alpine grasslands while 8.1% area is under agriculture. Degraded forest covers maximum area (53 km²), followed by moderately (30.4 km²) and severely degraded (26.8 km²) forests. The lower and middle slopes showed higher degradation than upper slopes due to multiple uses for agriculture, horticulture, agroforestry and grazing by the local people. Over time, the degradation and deforestation, without adequate protection, have led to severe soil erosion, biodiversity and the habitat depletion for a large number of rare and endemic species including loss of livelihood to the local people.     

Influence of hydrology process on wetland landscape pattern: A case study in the Yellow River Delta

A comprehensive study using ecological engineering analysis was conducted on the influence of the hydrology process in the Yellow River Delta. It was found that water and sediment played an important role in the formation and maintenance of the estuarine wetland. Based on hydrological data (1950–2005), meteorological data (1954–2005) and landscape data produced from integrated Landsat TM images of the Yellow River Delta, the relationship among all the above factors has been analyzed. The results indicated that runoff, sediment discharge and the area of the reed marsh wetland, meadow wetland and tidal wetland had evidently decreased from 1986 to 2001. The runoff and sediment discharge into the Yellow River Delta at a rate of 200–300 × 10⁸ m³ and at 5–8 × 10⁸ t, respectively, were probably the most optimal range for maintaining the stable wetland landscape pattern. Regression analysis and principal component analysis showed that there was a strong positive correlation between the area of wetland landscape and runoff, sediment discharge, whereas there was a negative correlation between the area and the temperature, and there was no significant trend with precipitation levels. The water and sediment discharge are the dominant variable factors of the wetland. Human activities also have an important influence on transformation of wetland types as well as wetland degradation. Therefore, with economic development, climate change and sustainable utilization of resources, great attention should be paid to the changes of natural landscape and their causes.     

Two-decade wetland cultivation and its effects on soil properties in salt marshes in the Yellow River Delta,China

Wetland cultivation and its effects on soil properties in salt marshes in the Yellow River Delta, China were examined by using a combination of the satellite imageries and field experiments. Results showed that the conversions mainly occurred between dry lands and Phragmites australis–Suaeda salsa–Tamarix chinensis marshes (PSTMs). The total area of marsh wetland was reduced by 65.09 km² during the period from 1986 to 2005, and these conversions might be attributed to a combination of farming, oil exploration and water extraction, as well as soil salinization. Significant differences were observed in bulk density, pH, salinity and NO₃⁻-N between different land-use types (P < 0.05). After the conversions from marsh wetlands to dry lands, bulk density, pH, salinity and NH₄⁺-N decreased slightly, while a significant increase in NO₃⁻-N, TN (total nitrogen), and AP (available phosphorus) (P < 0.05) was observed. The more loss of soil nutrient storage also occurred after the maximal area conversion from PSTMs to dry lands compared to other conversions during the study period. The storages of soil organic matter, NH₄⁺-N and total phosphorus decreased greatly under the conversion from three types of marshes to dry lands, while those of NO₃⁻-N, AP and TN showed an obvious increase during the whole study period.     

Monitoring fragile upland landscapes: The application of airborne lidar

This paper investigates the potential of airborne lidar for recording and monitoring erosion levels in environmentally fragile upland landscapes, using an area of the Brecon Beacons National Park as a case study. Upland areas contain a rich variety of natural and cultural resources that are increasingly endangered through factors such as insensitive land-use practices, improvements in recreational access and climate change. Airborne lidar provides a highly detailed record of microtopography, in this example at a resolution of 0.5 m with a vertical accuracy of c.0.15 m and the ability to differentiate elevation changes to within 1-2 cm. The technique therefore allows the rapid and cost-effective recording of the nature and extent of erosion at a landscape scale, with the results of this analysis recording over 46 kilometres of path erosion within a 3.8 km² area. The technique also provides the ability to highlight particular areas of risk, such as extensive braided erosion around path intersections and damage to protected SSSI habitats, providing a snapshot record of erosion at a particular point in time and an invaluable source of information for conservationists and policy-makers.     

Detection of sensitive soil properties related to non-point phosphorus pollution by integrated models of SEDD and PLOAD

Effectively identifying soil properties in relation to non-point source (NPS) phosphorus pollution is important for NPS pollution management. Previous studies have focused on particulate P loads in relation to agricultural non-point source pollution. In areas undergoing rapid urbanization, dissolved P loads may be important with respect to conditions of surface infiltration and rainfall runoff. The present study developed an integrated model for the analysis of both dissolved P and particulate P loads, applied to the Meiliang Bay watershed, Taihu Lake, China. The results showed that NPS P loads up to 15 kg/km² were present, with particulate P loads up to 13 kg/km². The highest loads were concentrated in the southeastern region of the watershed. Although particle P was the main contributor to NPS P loads state, the contribution of dissolved P was significant, especially in sub-basins with significant amount of artificial land cover. The integration of dissolved P and particulate P loads provided more accurate evaluation of NPS P pollution. NPS P loads were found to correspond to specific soil properties. Soil organic matter and total nitrogen were shown to influence dissolved P loads, while total phosphorus and soil particle composition proportion were more closely related to particulate P loads.     

Response of native grasses and Cicer arietinum to soil polluted with mining wastes: Implications for the management of land adjacent to mine sites

Mine tailings are an environmental problem in Southern Spain because wind and water erosion of bare surfaces results in the dispersal of toxic metals over nearby urban or agricultural areas. Revegetation with tolerant native species may reduce this risk. We grew two grasses, Lygeum spartum and Piptatherum miliaceum, and the crop species Cicer arietinum (chickpea) under controlled conditions in pots containing a mine tailings mixed into non-polluted soil to give treatments of 0%, 25%, 50%, 75% and 100% mine tailings. We tested a neutral (pH 7.4) mine tailings which contained high concentrations of Cd, Cu, Pb and Zn. Water-extractable metal concentrations increased in proportion to the amount of tailings added. The biomass of the two grasses decreased in proportion to the rate of neutral mine-tailing addition, while the biomass of C. arietinum only decreased in relation to the control treatment. Neutron radiography revealed that root development of C. arietinum was perturbed in soil amended with the neutral tailings compared to those of the control treatment, despite a lack of toxicity symptoms in the shoots. In all treatments and for all metals, the plants accumulated higher concentrations in the roots than in shoots. The highest concentrations occurred in the roots of P. miliaceum (2500 mg kg^?1 Pb, 146 mg kg^?1 Cd, 185 mg kg^?1 Cu, 2700 mg kg^?1 Zn). C. arietinum seeds had normal concentrations of Zn (70–90 mg kg^?1) and Cu (6–9 mg kg^?1). However, the Cd concentration in this species was ～1 mg kg^?1 in the seeds and 14.5 mg kg^?1 in shoots. Consumption of these plant species by cattle and wild fauna may present a risk of toxic metals entering the food chain.     

The role of plants in the removal of nutrients at a constructed wetland treating agricultural (dairy) wastewater,Ontario, Canada

The South Nation River Watershed, in eastern Ontario, Canada, is an agricultural watershed impacted by excess nutrient loading primarily from agricultural activities. A constructed wetland for the treatment of agricultural wastewater from a 150-cow dairy operation in this watershed was monitored in its eighth operating season to evaluate the proportion of total nitrogen (TN) (approximated by total Kjeldahl nitrogen (TKN) due to low NO₃⁻) and total phosphorus (TP) removal that could be attributed to storage in Typha latifolia L. and Typha angustifolia L., which dominate this system. Nutrient loading rates were high, with 16.2 kg ha⁻¹ d⁻¹ N and 3.4 kg ha⁻¹ d⁻¹ P entering the wetland and loading the first wetland cell. Plant uptake accounted for 0.7% of TKN removal when the vegetated free water surface cells were considered together. However, separately, in the second wetland cell with lower N and P loading rates, plants accounted for 9% of TKN, 21% of NH₄⁺ and 5% of TP removal. Plant uptake was significant to overall removal given wetland age and nutrient loading. Nutrient storage during the growing season at this constructed wetland helped reduce the nutrient load entering the watershed, already stressed by intensive local agriculture.     

Valuation of the loss of plant-related ecosystem services caused by water stress in the wetland of China’s Yellow River Delta

China’s Yellow River Delta is ecologically important because of its role as an eco-tone between terrestrial and aquatic ecosystems. However, water stress caused by drought or flooding creates ecological risks for this important ecosystem. In this study, we assessed community biodiversity, plant biomass, and the plant total nitrogen, total phosphorus, and potassium contents to quantify the potential loss of ecosystem services value arising from water stress. The annual ecosystem services and function value of the wetlands totaled 3.68 × 10⁸ Yuan, of which biomass production and local climate regulation accounted for 39.4% and 49.5% of the total, respectively. The area with the highest value (>2 Yuan m⁻²) lies along both banks of the downstream reaches of the river, whereas areas with the lowest values (<1.5 Yuan m⁻²) were located on the northern bank, near the Bohai Sea coastline. We defined scenarios based on three levels of water stress: drought, sufficient water, and flooding. The potential annual value loss in the drought scenario was 3.60 × 10⁸ Yuan, versus 2.78 × 10⁸ Yuan in the flooding scenario. The minimum loss (with sufficient water) was 2.06 × 10⁸ Yuan. The wetland’s soil water content should therefore be managed to protect the vegetation and minimize the ecological risks (and associated ecosystem service value losses) caused by water stress. Our approach provides a tool for assessing the potential loss of ecosystem services and functions and for calculating ecological compensation payments for wetland damage.     

Modeling WEPP erodibility parameters in calcareous soils in northwest Iran

Modeling soil detachment rates at the regional scale is important for better understanding of the processes of erosion and the development of erosion models. Soil erodibility is an important factor for predicting soil loss, but its direct measurement at the watershed scale is difficult, time-consuming and costly. This study used stepwise multiple-linear regression (MLR) and artificial neural networks (ANNs) to model Water Erosion Prediction Project (WEPP) soil erodibility parameters, including the baseline inter-rill erodibility (K_ib), baseline rill erodibility (K_rb) and critical shear stress (τ_cb) of cropland conditions in calcareous soils of northwest Iran. Simulated inter-rill and rill erosion experiments were conducted at 100 locations with three replications. K_ib, K_rb and τ_cb and basic soil properties were measured at each location. Auxiliary variables related to soil erodibility were derived from a Landsat 7 satellite image and a 30 m × 30 m digital elevation model (DEM). MLR and ANN models were employed to predict K_ib, K_rb and τ_cb using two groups of input variables: i) more easily measurable basic soil properties (pedo-transfer functions (PTFs)) and ii) more easily measurable basic soil properties and auxiliary data (soil spatial prediction functions (SSPFs)). The results indicated that the WEPP models performed poorly in comparison to the derived models. PTFs and SSPFs generated from ANN models provided more reliable predictions than the MLR models. ANN-based SSPF models yielded the best results (with the highest R² and lowest RMSE values) for predicting Kib and Krb. ANN-based PTF model performed reasonably well for predicting τ_cb. These results show that information from terrain attributes and remote sensing data are potential auxiliary variables for improving prediction of soil erodibility parameters.     

Effects of urban and non-urban land cover on nitrogen and phosphorus runoff to Chesapeake Bay

The aim of this study was to determine the effects of catchment and riparian stream buffer-wide urban and non-urban land cover/land use (LC/LU) on total nitrogen (TN) and total phosphorus (TP) runoff to the Chesapeake Bay. The effects of the composition and configuration of LC/LU patches were explored in particular. A hybrid-statistical-process model, the SPAtially Referenced Regression On Watershed attributes (SPARROW), was calibrated with year 1997 watershed-wide, average annual TN and TP discharges to Chesapeake Bay. Two variables were predicted: (1) yield per unit watershed area and (2) mass delivered to the upper estuary. The 166,534 km² watershed was divided into 2339 catchments averaging 71 km². LC/LU was described using 16 classes applied to both the catchments and also to riparian stream buffers alone. Seven distinct landscape metrics were evaluated. In all, 167 (TN) and 168 (TP) LC/LU class metric combinations were tested in each model calibration run. Runs were made with LC/LU in six fixed riparian buffer widths (31, 62, 125, 250, 500, and 1000 meters (m)) and entire catchments. The significance of the non-point source type (land cover, manure and fertilizer application, and atmospheric deposition) and factors affecting land-to-water delivery (physiographic province and natural or artificial land surfaces) was assessed. The model with a 31 m riparian stream buffer width accounted for the highest variance of mean annual TN (r² = 0.9366) and TP (r² = 0.7503) yield (mass for a specified time normalized by drainage area). TN and TP loadings (mass for a specified time) entering the Chesapeake Bay were estimated to be 1.449 × 10⁸ and 5.367 × 10⁶ kg/yr, respectively. Five of the 167 TN and three of the 168 TP landscape metrics were shown to be significant (p-value ≤ 0.05) either for non-point sources or land-to-water delivery variables. This is the first demonstration of the significance of riparian LC/LU and landscape metrics on water quality simulation in a watershed as large as the Chesapeake Bay. Land cover metrics can therefore be expected to improve the precision of estimated TN and TP annual loadings to the Chesapeake Bay and may also suggest changes in land management that may be beneficial in control of nutrient runoff to the Chesapeake Bay and similar watersheds elsewhere.     

Population densities,group size and biomass of ungulates in a lowland tropical rainforest forest of the eastern Himalayas

Large ungulate population monitoring is a crucial wildlife management tool as ungulates help in structuring and maintaining the large carnivore populations. Reliable data on population status of major ungulate prey species are still non-existent for most of the protected areas in the Indian part of the eastern Himalayan biodiversity hotspot. Twenty transects were monitored over a period of three years (2009–2011) totaling 600 km with an average length of 2 km. The estimated mean density of ungulates was 17.5 km⁻² with overall density of 48.7 km⁻². The wild pig Sus scrofa had the highest density (6.7 ± 1.2 km⁻²) among all the prey species followed by barking deer Muntiacus muntjak (3.9 ± 0.6 km⁻²), sambar Rusa unicolor (3.8 ± 0.5) and gaur Bos gaurus (3.5 ± 0.9 km⁻²). The estimated total ungulate biomass density was 2182.56 kg km⁻². This prey biomass can support up to 7.2 tigers per 100 km⁻². However, with two other sympatric carnivores sharing the same resources, the actual tiger numbers that can be supported will be lower. The estimated minor prey species was 31 km⁻² significantly 30.6% crop damages were reported by wild pig (p = 0.01) and 35.4% was elephant (p = 0.004). This data on ungulate densities and biomass will be crucial for carnivore conservation in this understudied globally significant biodiversity hotspot.     

Variation of soil nutrients and particle size under different vegetation types in the Yellow River Delta

The Yellow River Delta wetland, located at the southern coast of Bohai Gulf, provides important ecosystem services such as flood control, water purification, biodiversity conservation, nutrient removal and carbon sequestration, shoreline stabilization, tourism attraction and wetland products maintains in the Yellow River Delta. This study assessed how agricultural activities in a reclamation wetland changed soil pH, soil electric conductivity, soil nutrient and soil particle size as compared to natural vegetation by using a combination of field experiments and lab analysis. The vegetation type included adjacent alfalfa field (Medicago sativa), cotton field (Gossypium spp.), Chinese tamarisk shrub (Tamarix chinensis), and reed marsh (Phragmites sage). The results indicated that the soil pH was higher (pH > 8) in alfalfa field and cotton field, and alfalfa field and reed marsh had significant function in reducing soil salt content, soil electric conductivity of alfalfa field at 0–30 cm were 140.38 ± 14.36, 114.48 ± 14.36, 125.30 ± 11.37 μs/cm. The effect of different vegetation types on soil nutrient was significant (P < 0.05). Soil organic matter at 0–10 cm in Chinese tamarisk shrub and reed marsh was 21.66 ± 3.82 g/kg and 16.51 ± 4.60 g/kg, which was higher than that of alfalfa field (10.47 ± 2.36 g/kg) and cotton field (9.82 ± 1.27 g/kg), but soil total nitrogen content in alfalfa field was the highest, which is significantly higher than that of cotton field, Chinese tamarisk shrub and reed marsh(P < 0.05), the content of soil total nitrogen at 0–10 cm and 10–20 cm was 7.67 ± 0.38 g/kg and 5.97 ± 0.51 g/kg, respectively, while the content of available P and available K was reversed. The difference of soil particle size between layers was not significant (P > 0.05), the sand content of Chinese tamarisk shrub soils in 0–10 cm was the highest, the next was alfalfa field and cotton field, and the content of silt and clay in reed marsh was higher than the others. The correlation and significant degree between soil particle size and soil nutrient was related with vegetation types, and soil organic matter was significantly positively correlated with soil silt and clay content on the alfalfa field. The results demonstrated that wetland cultivation was one of the most important factors influencing on the nutrient fate and reserves in soil, which could lead to rapid nutrient release and slow restoration through abandon cultivation. Consequently, compared with cotton field, alfalfa field is more favorable to sustainable management of wetland cultivation in the Yellow River Delta. It should be considered in wetland restoration projects planning.     

Nitrate-nitrogen retention in wetlands in the Mississippi River Basin

Nitrate-nitrogen retention as a result of river water diversions is compared in experimental wetland basins in Ohio for 18 wetland-years (9 years × 2 wetland basins) and a large wetland complex in Louisiana (1 wetland basin × 4 years). The Ohio wetlands had an average nitrate-nitrogen retention of 39 g-N m⁻² year⁻¹, while the Louisiana wetland had a slightly higher retention of 46 g-N m⁻² year⁻¹ for a similar loading rate area. When annual nitrate retention data from these sites are combined with 26 additional wetland-years of data from other wetland sites in the Basin Mississippi River (Ohio, Illinois, and Louisiana), a robust regression model of nitrate retention versus nitrate loading is developed. The model provides an estimate of 22,000 km² of wetland creation and restoration needed in the Mississippi River Basin to remove 40% of the nitrogen estimated to discharge into the Gulf of Mexico from the river basin. This estimated wetland restoration is 65 times the published net gain of wetlands in the entire USA over the past 10 years as enforced by the Clean Water Act and is four times the cumulative total of the USDA Wetland Reserve Program wetland protection and restoration activity for the entire USA.