Impact of riparian buffer zones on water quality and associated management considerations

Recent attention has focused on riparian forest buffer systems for filtering sediment, nutrients, and pesticides entering from upland agricultural fields. This paper summarizes the results of a field monitoring study done in Tokachikawa watershed in Hokkaido, Japan, Cisadane, Cianten and Citamyang sub-watersheds in Indonesia and Cauvery watershed, India to quantify the impact of riparian buffer zones on changes in stream water quality. A watershed approach was used to compare land use indicators – uplands, forests, riparian forest, livestock areas – to a wide range of surface water physical and chemical properties. Stream water physical property values increased from upstream to the confluence point, influenced by the upland and livestock land use activities. The greatest reduction in impairment of water quality was observed in buffer zones located along higher order streams where the gradient is very low, leading to slow groundwater movement. The lower stream water temperature in riparian buffer zones suggests that the shading effect is most pronounced in this area of the watershed. The results demonstrate the positive impact of forest buffer zones in reducing the influence of agricultural nutrients and chemicals on surface stream waters. Design and management considerations for establishing riparian zone land use are discussed.     

Relationship between Riparian Vegetation and Stream Benthic Communities at Three Spatial Scales

We examined the influence of riparian vegetation on macroinvertebrate community structure in streams of the Upper Thames River watershed in southwestern Ontario. Thirty-three μ-basins (129–1458 ha) were used to identify land cover variables that influenced stream macroinvertebrates. Micro-basins represented the entire drainage area of study streams and were similar in stream order (first, second) and land cover (agricultural or forest; no urban). We described the structure and composition of riparian vegetation and benthic macroinvertebrate communities at the outflow reach. The nature of the land cover was quantified for the stream network buffer (30 m) and the whole μ-basin. The objective of this study was to measure the magnitude and nature of the relationship between the riparian vegetation and benthic macroinvertebrate community at the outflow reach, stream network buffer, and whole μ-basin scales. Taxon richness (including total number of Ephemeroptera, Plecoptera, and Trichoptera taxa) and Simpson’s diversity of the macroinvertebrate community all increased with increased tree cover in the riparian zone at the outflow reach scale. Simpson’s equitability was lower with greater agricultural land cover in the stream network buffer. No relationship between the macroinvertebrate community and land cover was found at the whole μ-basin scale. Analysis of the influence of land cover on stream communities within a spatial hierarchy is important for understanding the interactions of stream ecosystems with their adjacent landscapes.     

Effect of Native Vegetation Loss on Stream Ecosystem Processes: Dissolved Organic Matter Composition and Export in Agricultural Landscapes

Stream and river ecosystems are dependent on energetic inputs from their watersheds and thus shifts in land use from forest cover to agriculture will affect stream community composition and function. The disruption of forest-aquatic linkages alters the organic matter resources in agricultural streams. Dissolved organic matter (DOM) is the dominant form of organic matter in aquatic ecosystems, and a microbial energy source that is important for stream respiration. The concentrations and characteristics of DOM are regulated by both terrestrial (for example, terrestrial organic matter supply) and in-stream processes (for example, microbial respiration and periphyton production) that are influenced by land management. The effects of watershed land use and topographic, soil and climatic variables on DOM quantity (dissolved organic carbon concentration and load), source (terrestrial or in-stream) and quality (composition and lability) were measured in 14 streams across an agricultural land-use gradient. DOC concentration was positively correlated with watershed pasture cover and negatively correlated with watershed relief. No watershed variables were important correlates of DOC load. Stream DOM was primarily of terrestrial origin, but DOM in agricultural streams had a greater proportion of sources from in-stream sources. This may be due to reduced connection with riparian vegetation and increased in-stream primary production. We suggest that maintaining watershed tree cover greater than 52% and ensuring less than 10% of the length of riparian corridor is cleared for pasture could minimize changes to DOM composition. This is important to avoid flow-on effects for stream ecosystem processes that are mediated by DOM. Long-term DOM monitoring will be valuable for assessing the functional impacts of land-use change.     

Planted Riparian Buffer Zones in New Zealand: Do They Live Up to Expectations?

Abstract River and stream rehabilitation projects are increasing in number, but the success or failure of these projects has rarely been evaluated, and the extent to which buffers can restore riparian and stream function and species composition is not well understood. In New Zealand the widespread conversion of forest to agricultural land has caused degradation of streams and riparian ecosystems. We assessed nine riparian buffer zone schemes in North Island, New Zealand that had been fenced and planted (age range from 2 to 24 years) and compared them with unbuffered control reaches upstream or nearby. Macroinvertebrate community composition was our prime indicator of water and habitat quality and ecological functioning, but we also assessed a range of physical and water quality variables within the stream and in the riparian zone. Generally, streams within buffer zones showed rapid improvements in visual water clarity and channel stability, but nutrient and fecal contamination responses were variable. Significant changes in macroinvertebrate communities toward “clean water” or native forest communities did not occur at most of the study sites. Improvement in invertebrate communities appeared to be most strongly linked to decreases in water temperature, suggesting that restoration of in‐stream communities would only be achieved after canopy closure, with long buffer lengths, and protection of headwater tributaries. Expectations of riparian restoration efforts should be tempered by (1) time scales and (2) spatial arrangement of planted reaches, either within a catchment or with consideration of their proximity to source areas of recolonists.     

Comparisons of P-Yield,Riparian Buffer Strips,and Land Cover inSix Agricultural Watersheds

Riparian buffer strips may protect streams from phosphorus (P) pollution. We compared 2 years of daily P-yield (μg m⁻² day⁻¹) from six southeast Wisconsin watersheds with contrasting riparian buffer attributes. Of the variables measured, mean daily P-yield was most closely correlated with the variability in riparian patch size. Variability in P-yield was most closely correlated with characteristics of the riparian buffer, such as percent wetland land cover, riparian continuity, and stream sinuosity. During the most extreme events, mean P-yield was negatively correlated with the percentage of wetland land cover in the upland watershed. Correlations suggest that riparian continuity may influence P-loading in these watersheds. Our results corroborate the importance of continuity and uniformity of riparian buffers as moderators of P flow from upland agricultural lands into streams. Received 1 June 2001; accepted 5 February 2002.     

Catchment morphometric characteristics,land use and water chemistry in Pampean streams: a regional approach

The Pampean region covers a large surface in central Argentina, but despite the extensive agricultural activities and the high nutrient levels recorded in streams of the region, few authors have analysed the influence of land use on water quality. Here, we evaluated the relationships among catchment attributes (size, morphometry and land cover) and water chemistry in 23 Pampean streams in different seasons (autumn, spring and summer) and at three spatial scales: whole catchment and two scales of riparian buffers (200 and 500 m adjacent to both stream margins). Chloride concentration was positively related to catchment area and negatively related to drainage density. Nitrate level was strongly associated to cropland, but soluble phosphorus concentration showed no relationships with any type of land cover. Land cover at the buffer scale seemed to be more influential than land cover at the whole catchment for nitrogen concentration. The main impact of cropland was the increase of nitrate concentration, while cattle breeding was negatively associated to photosynthetically active radiation (PAR) in autumn and summer and to dissolved oxygen concentration in spring. Our results highlighted the importance of local land use and riparian conservation on streamwater quality.     

美国大陆五个山区集水区的河溪结构分析

河溪结构及其关联的空间特征,是研究集水区中能量和物质移动规律所不可缺少的内容,利用美国地质调查局的水文数据库和地理信息系统（ＡＲＣ／ＩＮＦＯ）,对美国大陆５个主要山地中典型集水区河溪的数据量、密度,分布结构以及河溪岸边带的组成,进行了分析和比较。５个山地分别是：西北太平洋沿岸,西部卡斯卡特山,中部落矶山,东部阿巴拉契亚山和南部欧扎克山,发现这５个集水区中的河溪网络结构非常相似,一级河溪大约占河溪总     

SPATIAL PATTERNS AND ECOLOGICAL DETERMINANTS OF BENTHIC ALGAL ASSEMBLAGES IN MID-ATLANTIC STREAMS, USA

We attempted to identify spatial patterns and determinants for benthic algal assemblages in Mid-Atlantic streams. Periphyton, water chemistry, stream physical habitat, riparian conditions, and land cover/use in watersheds were characterized at 89 randomly selected stream sites in the Mid-Atlantic region. Cluster analysis (TWINSPAN) partitioned all sites into six groups on the basis of diatom species composition. Stepwise discriminant function analysis indicated that these diatom groups can be best separated by watershed land cover/use (percentage forest cover), water temperature, and riparian conditions (riparian agricultural activities). However, the diatom-based stream classification did not correspond to Omernik's ecoregional classification. Algal biomass measured as chl a can be related to nutrients in habitats where other factors do not constrain accumulation. A regression tree model indicated that chl a concentrations in the Mid-Atlantic streams can be best predicted by conductivity, stream slope, total phosphorus, total nitrogen, and riparian canopy coverage. Our data suggest that broad spatial patterns of benthic diatom assemblages can be predicted both by coarse-scale factors, such as land cover/use in watersheds, and by site-specific factors, such as riparian conditions. However, algal biomass measured as chl a was less predictable using a simple regression approach. The regression tree model was effective for showing that ecological determinants of chl a were hierarchical in the Mid-Atlantic streams.     

Deforestation and Benthic Indicators: How Much Vegetation Cover Is Needed to Sustain Healthy Andean Streams?

Deforestation in the tropical Andes is affecting ecological conditions of streams, and determination of how much forest should be retained is a pressing task for conservation, restoration and management strategies. We calculated and analyzed eight benthic metrics (structural, compositional and water quality indices) and a physical-chemical composite index with gradients of vegetation cover to assess the effects of deforestation on macroinvertebrate communities and water quality of 23 streams in southern Ecuadorian Andes. Using a geographical information system (GIS), we quantified vegetation cover at three spatial scales: the entire catchment, the riparian buffer of 30 m width extending the entire stream length, and the local scale defined for a stream reach of 100 m in length and similar buffer width. Macroinvertebrate and water quality metrics had the strongest relationships with vegetation cover at catchment and riparian scales, while vegetation cover did not show any association with the macroinvertebrate metrics at local scale. At catchment scale, the water quality metrics indicate that ecological condition of Andean streams is good when vegetation cover is over 70%. Further, macroinvertebrate community assemblages were more diverse and related in catchments largely covered by native vegetation (>70%). Our results suggest that retaining an important quantity of native vegetation cover within the catchments and a linkage between headwater and riparian forests help to maintain and improve stream biodiversity and water quality in Andean streams affected by deforestation. This research proposes that a strong regulation focused to the management of riparian buffers can be successful when decision making is addressed to conservation/restoration of Andean catchments.     

Riverine invertebrate assemblages are degraded more by catchment urbanisation than by riparian deforestation

1. Restoration of riparian forests has been promoted as a means of mitigating urban impacts on stream ecosystems. However, conventional urban stormwater drainage may diminish the beneficial effect of riparian forests.
2. The relative effects of riparian deforestation and catchment urbanisation on stream ecosystems have rarely been discriminated because urban land use and riparian degradation usually covary. However, land use at three scales (channel canopy cover along a 100-m site, riparian forest cover within 200 m of the channel for 1 km upstream, and catchment imperviousness) covaried only weakly along the lowland Yarra River, Victoria, Australia.
3. We tested the extent to which each land use measure explained macroinvertebrate assemblage composition on woody debris and in the sediments of pools or runs in the mainstem Yarra River in autumn and spring 1998.
4. Assemblage composition in both habitats and in both seasons was most strongly correlated with proportion of catchment covered by impervious surfaces. Sites with higher imperviousness had fewer sensitive taxa (those having a strong positive influence on indicators of biological integrity) and more taxa typical of degraded urban streams. Sensitive taxa rarely occurred in sites with >4% total imperviousness. However, within sites of similar imperviousness, those with more riparian forest cover had more dipteran taxa. Channel canopy cover did not explain assemblage composition strongly.
5. Riparian forest cover may influence richness of some macroinvertebrate taxa, but catchment urbanisation probably has a stronger effect on sensitive taxa. In catchments with even a small amount of conventionally drained urban land, riparian revegetation is unlikely to have an effect on indicators of stream biological integrity. Reducing the impacts of catchment urbanisation through dispersed, low-impact drainage schemes is likely to be more effective.     

不同空间尺度的景观格局对流溪河水质的影响

为探究不同空间尺度的景观格局对流溪河水质的影响,于2020年6月和2021年1月在流溪河干流15个采样点进行了水样的采集,测定了水温、溶解氧、pH、氨氮、硝态氮、硫酸盐和氯化物等水质指标。结合遥感解译所得的土地利用数据,提取了不同空间尺度(子流域和河岸带缓冲区)的景观格局指数,采用Bioenv分析、Mantle检验、方差分解和层次分割理论等方法揭示了景观格局对水质变化的影响。研究结果表明：氨氮是流溪河的主要污染物。土地利用结构与空间格局特征对水质的影响存在空间尺度效应。在100 m河岸带缓冲区,水域是影响水质的主要贡献源;而在其他空间尺度建设用地是影响水质的主要贡献源。在子流域尺度,林地和建设用地的斑块密度(PD指数)是影响水质变化的核心特征;而在河岸带缓冲区尺度,水域和建设用地的连通性(CONTAG指数)和林地的多样性(SHDI指数)是影响水质变化的关键特征。在各个空间尺度,土地利用与空间格局的交互作用对驱动水质变化起主导作用,尤其在1000 m河岸带缓冲区对水质的贡献率最高。因此,加强1000 m缓冲区尺度土地利用的管理和减少建设用地成片建设规划等对保护流域水质具有重要意义。     

Relationships between land use, spatial scale and stream macroinvertebrate communities

1. The structure of lotic macroinvertebrate communities may be strongly influenced by land‐use practices within catchments. However, the relative magnitude of influence on the benthos may depend upon the spatial arrangement of different land uses in the catchment. 2. We examined the influence of land‐cover patterns on in‐stream physico‐chemical features and macroinvertebrate assemblages in nine southern Appalachian headwater basins characterized by a mixture of land‐use practices. Using a geographical information system (GIS)/remote sensing approach, we quantified land‐cover at five spatial scales; the entire catchment, the riparian corridor, and three riparian ‘sub‐corridors’ extending 200, 1000 and 2000 m upstream of sampling reaches. 3. Stream water chemistry was generally related to features at the catchment scale. Conversely, stream temperature and substratum characteristics were strongly influenced by land‐cover patterns at the riparian corridor and sub‐corridor scales. 4. Macroinvertebrate assemblage structure was quantified using the slope of rank‐abundance plots, and further described using diversity and evenness indices. Taxon richness ranged from 24 to 54 among sites, and the analysis of rank‐abundance curves defined three distinct groups with high, medium and low diversity. In general, other macroinvertebrate indices were in accord with rank‐abundance groups, with richness and evenness decreasing among sites with maximum stream temperature. 5. Macroinvertebrate indices were most closely related to land‐cover patterns evaluated at the 200 m sub‐corridor scale, suggesting that local, streamside development effectively alters assemblage structure. 6. Results suggest that differences in macroinvertebrate assemblage structure can be explained by land‐cover patterns when appropriate spatial scales are employed. In addition, the influence of riparian forest patches on in‐stream habitat features (e.g. the thermal regime) may be critical to the distribution of many taxa in headwater streams draining catchments with mixed land‐use practices.     

Landscape diversity and forest edge density regulate stream water quality in agricultural catchments

It is well known that the composition of land cover within a watershed plays a large role in regulating stream water quality. However, there remains significant uncertainty regarding the effect of spatial configuration of different types of land cover on water quality. Using periphytic algae (diatoms) as indicators of stream trophic state, we investigated the relationship between landscape configuration and water quality in a large number of watersheds (590) at varying catchment scales in Eastern Canada. Variation partitioning analysis showed that landscape configuration explained 48% of the variation in water quality. However, since the physiographic setting constrains most agricultural activities, most of the variation was attributed to the shared influence of surficial deposits, land cover and landscape configuration (34%). The results from regression models showed that the geomorphological setting of watersheds (surficial deposits and slopes) and the proportion of different land cover types (mainly forests, wetlands, crops and urban areas) have a major impact on stream water quality. Nevertheless, a few configuration metrics emerged as important factors. Landscape diversity appeared to have a negative impact on water quality, whereas forest and wetland edge densities had a positive impact. Moreover, the influence of these lanscape metrics seems to occur at certain thresholds. In areas of intensive farming, streams with a forest area that covers at least 47% of the watershed have a better water quality. Below this threshold, eutrophic and meso-eutrophic conditions are more frequent in streams and rivers. The shape and location of forested patches were also found to be relevant. Woodlands and wetlands with an edge density higher than 36 m/ha and located along streams and gullies have a positive impact on water quality. For the same proportion of forest, complex patches will be more efficient filters than large regular patches. Forest edge density seems to control the extent of the interface with the agricultural sources and thus promotes the “sink” effect of forests on nutrients.     

Fire and Grazing Influences on Rates of Riparian Woody Plant Expansion along Grassland Streams

Grasslands are threatened globally due to the expansion of woody plants. The few remaining headwater streams within tallgrass prairies are becoming more like typical forested streams due to rapid conversion of riparian zones from grassy to wooded. Forestation can alter stream hydrology and biogeochemistry. We estimated the rate of riparian woody plant expansion within a 30 m buffer zone surrounding the stream bed across whole watersheds at Konza Prairie Biological Station over 25 years from aerial photographs. Watersheds varied with respect to experimentally-controlled fire and bison grazing. Fire frequency, presence or absence of grazing bison, and the historical presence of woody vegetation prior to the study time period (a proxy for proximity of propagule sources) were used as independent variables to predict the rate of riparian woody plant expansion between 1985 and 2010. Water yield was estimated across these years for a subset of watersheds. Riparian woody encroachment rates increased as burning became less frequent than every two years. However, a higher fire frequency (1–2 years) did not reverse riparian woody encroachment regardless of whether woody vegetation was present or not before burning regimes were initiated. Although riparian woody vegetation cover increased over time, annual total precipitation and average annual temperature were variable. So, water yield over 4 watersheds under differing burn frequencies was quite variable and with no statistically significant detected temporal trends. Overall, burning regimes with a frequency of every 1–2 years will slow the conversion of tallgrass prairie stream ecosystems to forested ones, yet over long time periods, riparian woody plant encroachment may not be prevented by fire alone, regardless of fire frequency.     

Linkages among land-use, water quality, physical habitat conditions and lotic diatom assemblages: A multi-spatial scale assessment

We assessed the importance of spatial scales (catchment, stream network, and sample reach) on the effects of agricultural land-use on lotic diatom assemblages along a land-use gradient in the agricultural Willamette Valley Ecoregion of Oregon. Periphyton, water chemistry, and physical habitat conditions were characterized for 25 wadeable streams during a dry season (July to September, 1997). Additional water chemistry samples were collected in the following wet season (February 1998) to assess seasonal effects of land-use on stream water chemistry. Percent agricultural land-use in the study catchments ranged from 10% to 89% with an average of 52%. Partial canonical correspondence analysis (CCA) with the first axis constrained by % agricultural land-use showed that % agricultural land-use at 3 spatial scales explained between 3.7%–6.3% of variability in the diatom species dataset. Monte Carlo Permutation tests indicated that the variance explained by % agricultural land-use was only significant at the spatial scale of the stream network with 10- and 30-m band width (p<0.05, 999 permutations). In addition to the effects of % agricultural land-use, partial CCAs with a forward selection option showed that water chemistry (e.g., SiO₂), reach-scale stream channel dimensions (e.g., width, depth, and slope), reach-scale in-stream habitats (substrates and filamentous algal cover in stream beds), and riparian vegetative buffer were all important with relation to diatom species assemblages. Percent of obligately nitrogen-heterotrophic taxa was the only diatom autecological metric that showed a significant but weak correlation with % agricultural land-use along the stream network (r=0.50), but not at catchment or sample reach scale. Correlation between % agricultural land-use and water chemistry variables varied among the spatial scales and between seasons. Physical habitat variables (log₁₀ erodible substrate diameters and stream reach slope) were significantly correlated with % agricultural land-use along the stream network but not at catchment or sample reach scale. Our data suggest that spatial scales are important in assessing effects of land-use on stream conditions but the spatial scale effects may vary between seasons. Direct linkages between agricultural land-use and lotic diatom assemblages were weak during summer base-flow time regardless of the spatial scales. Summer sampling may underestimate the effects of catchment land-use on stream conditions in areas where seasonal patterns are so distinctive as in the Willamette Valley.     

不同空间尺度景观特征对南流江水质的影响差异

流域景观特征决定了非点源污染物来源与地表景观削减消纳能力,但尚缺乏全流域不同空间尺度对二者关联性的认识。以广西北部湾南流江为例,分别在子流域、河岸缓冲带以及监测点圆形缓冲区三种尺度上,基于2020年Landsat 8 OLI遥感影像解译的土地利用类型特征,结合水质监测数据,运用数理统计和GIS空间分析方法,探讨了流域景观特征在不同空间尺度上对河流水质的影响。结果表明：(1)在子流域尺度,土地利用类型以林地为主,而在河岸缓冲带与监测点圆形缓冲区均以耕地为主;(2)水质指标高锰酸盐指数、生化需氧量与景观特征相关性最为显著,耕地、建设用地、其他用地和园地与其呈正相关,是南流江水质污染负荷的重要来源区;景观格局指数中,斑块密度、蔓延度指数、多样性指数、均匀度指数是引起河流水质指标变化的主要景观因子;(3)受流域内或不同子流域间景观特征差异,景观组成面积占比和景观格局指数均在河岸缓冲带尺度对水质状况影响最大,分别可解释57.0%和64.7%的水质指标变化;子流域尺度次之,圆形缓冲区尺度最小,且景观格局指数对水质状况的影响大于景观组成面积占比。建议在河岸带50 m范围内严格控制耕地面积,建设河岸缓...     

SWAT模型对景观格局变化的敏感性分析——以丹江口库区老灌河流域为例

景观的空间配置与类型组成能够对流域的产流、产沙及非点源污染产生影响。在以往SWAT模型研究中,往往默认水文模型考虑了该影响。为分析SWAT模型对不同景观格局变化的敏感性,根据老灌河流域2000年土地利用在各子流域的组成,模拟研究区更为破碎、复杂的景观空间配置,通过设置多套试验参数,利用SWAT模型生成基于不同景观格局的模拟结果。结果表明,SWAT模型不能反映除坡度和面积变化之外的景观水平下各斑块之间因景观空间格局改变对流域产流、产沙以及非点源污染的影响;模型通过其他参数的调整,弥补了模型分析数据的不足,使实测数据与模型部分结果高度吻合。这表明,一个能够反映流域部分水文特征的SWAT模型,未必是对研究区真实情形的模拟,而是各个参数间平衡的结果。因此,在利用SWAT模型分析模拟景观变化时,不应默认模型能够模拟景观空间格局改变对流域水文过程的影响,同时研究者可以通过划分坡度带,提高模型对不同坡度土地利用的敏感性。     

Effect of land use types on stream water quality under seasonal variation and topographic characteristics in the Wei River basin,China

The effect of topographic characteristics of land uses on stream water quality must be addressed for a better understanding of the complex relationship between land use and stream water quality. In this study, Geographic Information System (GIS) and Pearson correlation analysis were used to determine whether there were relationship between land use types and stream water quality at the sub-basin scale in the Wei River basin, China, during the dry and rainy seasons in 2012. Temporal variation of these relations was observed, indicating that the relationships between water quality variables and different land uses were weaker in rainy seasons than that in dry seasons. Compared with other land uses, agriculture and urban lands had a stronger relationship with water quality variables in both rainy and dry seasons. Topographic characteristics of land use were employed to further analyze these relationships. The results showed that seasonal variation also occurred in the complex relationship, and land uses in steeper slopes generally had a stronger influence on stream water quality than those in flatter ones. For the riparian zone of each sampling site, the slope coefficients were weaker than those at the sub-basin scale. Land use type near stream water was generally a better indicator for the effectiveness of water quality. These results suggest that the slope and proximity should be taken into account for better land use management.     

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.     

Denitrification in the river network of a mixed land use watershed: unpacking the complexities

River networks have the potential to permanently remove nitrogen through denitrification. Few studies have measured denitrification rates within an entire river network or assessed how land use affect rates at larger spatial scales. We sampled 108 sites throughout the network of the Fox River watershed, Wisconsin, to determine if land use influence sediment denitrification rates, and to identify zones of elevated sediment denitrification rates (hot spots) within the river network. Partial least squares regression models identified variables from four levels of organization (river bed sediment, water column, riparian zone, and watershed) that best predicted denitrification rates throughout the river network. Nitrate availability was the most important predictor of denitrification rates, while land cover was not always a good predictor of local-scale nitrate concentrations. Thus, land cover and denitrification rate were not strongly related across the Fox River watershed. A direct relationship between denitrification rate and watershed land cover occurred only in the Wolf River sub-watershed, the least anthropogenically disturbed of the sub-watersheds. Denitrification hot spots were located throughout the river network, regardless of watershed land use, with hot spot location being determined primarily by nitrate availability. In the Fox River watershed, when nitrate was abundant, river bed sediment character influenced denitrification rate, with higher denitrification rates at sites with fine, organic sediments. These findings suggest that denitrification occurring throughout an entire river network, from headwater streams to larger rivers, can help reduce nitrogen loads to downstream water bodies.