Flood mapping with remote sensing and hydrochemistry: A new method to distinguish the origin of flood water during floods

River flooding is important for the ecological functioning of river floodplains. It is implicitly assumed that in many river floodplains during floods, river water is spreading all over the floodplain. We hypothesize that during flood events a spatial distribution of water types exists, which is correlated to different water sources (river water, atmospheric water and groundwater) and to the spatial distribution of vegetation types. The objective of this paper is to assess a new methodology to determine the extent of flooding and the spatial distribution of different water sources during the flood, using GPS, multispectral remote sensing and hydrochemical analyses. This methodology is applied to the Biebrza River Lower Basin, which has little human impact. Remote sensing resulted in a map distinguishing inundated areas from dry areas, which showed 85% agreement with GPS field measurements. Principal Component Analyses and Cluster Analyses on the measured water chemistry identified different water sources during the flood (river water, groundwater, rainwater) and showed the effects of human impact on water quality. River flood water dominated the entire inundation zone in the northern Lower Basin, which is narrower and steeper than the southern Lower Basin where groundwater and rainwater were significant contributors to the major part of the inundated area. Vegetation in the river flood zone is distinctly different from the rest of the floodplain. Due to mixing of ground- and rainwater, correlation analyses between vegetation and water type were not possible outside the river flood zone. The new methodology is effective in distinguishing inundated areas from dry regions and in separating river flood water from other water sources during a flood.     

Nitrogen cycling in two riparian forest soils under different geomorphic conditions

At the floodplain scale, spatial pattern and successional development of riparian vegetation are under the control of geomorphic processes. The geomorphic and hydraulic characteristics of stream channels affect the sorting of organic material and inorganic sediment through erosion/sedimentation during floods. In turn, the proportion of fine sediments fractions differs by location within a given community of riparian forest succession. In this paper we tested the effect of geomorphic features of floodplains, through soil grain size sorting, on the nitrogen cycling in riparian forest soils. Two typical riparian forests formed by vertical accretion deposits from repeated addition of sediments from overbank flow have been chosen along the River Garonne, southwest France. These riparian forests had equivalent vegetation, flood frequency and duration, differing only in soil grain size composition: one riparian forest had sandy soils and the other had loamy soils. The evolution of the main soil physical and chemical parameters as well as denitrification (DNT), N uptake (N _U ) and mineralization (N _M ) rates were measured monthly over a period of 13 months in the two study sites. The loamy riparian forest presented a better physical retention of suspended matter during floods. Moreover,in situ denitrification rates (DNT) and N uptake by plants (N _U ) measured in the loamy riparian forest soils were significantly greater than in the sandy soils. Although DNT and N _U could be in competition for available nitrogen, the peak rates of these two processes did not occur at the same period of the year, N _U being more important during the dry season when DNT was minimum, while DNT rates were maximum following the spring floods. N retention by uptake (N _U ) and loss by DNT represented together the equivalent of 32% of total organic nitrogen deposited during floods on the sandy riparian forest soils and 70% on the loamy ones. These significant differences between the two sites show that, at the landscape level, one should not estimate the rates of N _U and DNT, in riparian forests soils only on the basis of vegetation, but should take also into account the geomorphic features of the floodplain.     

Factors affecting the regeneration and distribution of riparian woodlands along a northern prairie river: the Red Deer River,Alberta, Canada

Abstract. Flooding patterns and variations in the composition and successional trends of riparian vegetation in the upper and lower Red Deer River in southern Alberta, Canada, were studied in order to establish which flood regimes were most important in the regeneration and maintenance of riparian vegetation communities, with a particular focus on riparian poplars. The dominant riparian tree in the upper river is Populus balsamifera with some Picea glauca and in the lower river Populus deltoides (the plains cottonwood). Dendrochronological studies of the poplars along the river show that major periods of regeneration correspond with major flood events during the record period. Extensive cottonwood regeneration occurred in the period 1900–20, corresponding with a series of floods, some as high as the 1 in 100-year event. In addition, just prior to and during this period there was a significant reduction in use of the floodplain by bison, clearance of forests and a higher incidence of fires in upper reaches of the river and a series of high rainfall years. A series of floods greater than the 1 in 10-year flood occurred in the 1950s and stimulated the most extensive regeneration of poplars experienced since the 1920s. Parts of the lower Red Deer floodplain are now at elevations well above the 1 in 100-year flood event. It is suggested that fringe replenishment of riparian poplars is currently the dominant form of regeneration and that the large stands of mature poplars found on the floodplain, initiated during the end of the last century and first decades of this century, are unlikely to be replaced unless large floods (>1 in 50-year events) occur again. Construction of the Dickson Dam above the city of Red Deer in 1983 has led to attenuation of floods and a reduced likelihood that extensive flooding and poplar regeneration will occur again. A number of recommendations are made regarding flow management to both retain the fringe regeneration of poplars currently occurring and to stimulate more widespread regeneration of poplars on the floodplain.     

Biogeochemical Constraints on the Ecological Rehabilitation of Wetland Vegetation in River Floodplains

The European policy for river management during peak discharge periods is currently changing from exclusion strategies (reinforcement of dykes) to allowing a more natural situation by creating more floodplain space to reduce water levels during peak discharges. In addition, water retention and water storage areas have been created. The new measures are generally being combined with nature development strategies. Up till now, however, ecological targets of broadscale floodplain wetland restoration including sedge marshes, species-rich floodplain forests and carrs, riparian mesotrophic grasslands and other biodiverse riverine ecosystems, have hardly developed in these areas. Most studies on the conditions needed for sustainable ecological development of floodplains have focused on hydrological and geomorphological rather than biogeochemical issues (including nutrient availability and limitation). There are, however, large differences in the composition of river water and groundwater and in sediment quality between rivers in densely populated areas and those in more pristine areas, which serve as a reference. It is very likely that these factors, in combination with heavily altered hydrological regimes and the narrow areas confined between the dykes on both sides of the rivers, impose major constraints on sustainable ecological development of riverine areas. Another issue is that existing wetlands are generally considered to be very appropriate for water retention and conservation, although recent research has shown that this may pose a serious threat to their biodiversity. The present paper reviews the biogeochemical constraints on the combination of floodplain rehabilitation, water conservation and the conservation and development of wetlands. It is concluded that biogeochemical problems (mainly related to eutrophication) predominantly arise in less dynamic parts of the river system, to which the flood-pulse concept applies less. Sound knowledge of the biogeochemical processes involved will contribute to greater efficiency and a better prediction of the opportunities for restoration and development of riverine wetlands. This information can be directly applied in nature management, water management, policy-making and consultancy.     

Effectiveness of a Newly Created Oxbow Lake to Mitigate Habitat Loss and Increase Biodiversity in a Regulated Floodplain

In 2005, an oxbow lake was constructed in a degraded floodplain area of the Ebro River (NE Spain) to mitigate habitat loss. In this study, we address the effectiveness of this restoration project through the analysis of the macroinvertebrate community that colonized the newly constructed lake, in comparison with a nearby natural oxbow lake and the adjacent river channel. To that end, water and macroinvertebrate samples were taken every 2 months in 2006. Ground movements during construction, wind‐driven bottom resuspension, shore scouring, and lack of vegetation resulted in distinctive water chemistry in the constructed and natural lakes. Regarding biodiversity, only 8 months after the digging of the constructed lake the abundance, richness, Shannon, and trait diversity of macroinvertebrates exceeded that of the natural lake. It is suggested that the constructed lake provided habitat for new mobile species that rapidly dispersed to other wetlands, thus enhancing the biological diversity of the floodplain at a local scale. Furthermore, biodiversity is predicted to continue increasing in the following years, although isolation can lead to early clogging of the system. By showing a dramatic increase in aquatic biodiversity in constructed wetlands, our study suggests that wetland construction can be very effective in mitigating habitat loss and increasing biodiversity in highly degraded floodplain areas. Further monitoring is nevertheless needed to evaluate the sustainability of the newly created habitat in the long term.     

Regional and global concerns over wetlands and water quality

Water quality in many stream catchments and river basins is severely impacted by nutrient enrichment as a result of agriculture. Water-resource managers worldwide are considering the potential role of riparian zones and floodplain wetlands in improving stream-water quality, as there is evidence at the site scale that such wetlands are efficient at removing nutrients from through-flowing water. However, recent studies have highlighted disadvantages of such use of wetlands, including emissions of greenhouse gases and losses of biodiversity that result from prolonged nutrient loading. Here, we discuss the water purification function of wetlands at the site and catchment scale and suggest ways in which these disadvantages could be overcome.     

Aquatic metabolism short-term response to the flood pulse in a Mediterranean floodplain

The pulsing of river discharge affects biodiversity and productivity of whole river–floodplain ecosystems, triggering the transport, storage and processing of carbon. In this study we investigate the short-term changes in water chemistry and net pelagic metabolism (NEP) in two floodplain lakes in response to a flood pulse. The two oxbow lakes investigated in the floodplain of the Mediterranean Ebro River (NE Spain) showed a clear temporal shift in their metabolic balance, controlled by the river discharge and associated changes in water physical and chemical characteristics. Water chemistry (turbidity, water organic matter, chlorophyll a and nutrients concentration) returned to pre-flood values after 4 days, highlighting the resilience of the ecosystem to flood pulses. Lake NEP was depressed before and during floods to a minimum of −34 mg O₂ m⁻³ h⁻¹, and increased after the flood pulse to a maximum of +463 mg O₂ m⁻³ h⁻¹. The phytoplankton assemblage showed before and after floods a replacement of autotrophic species (e.g. Chlorophyceans) by mixotrophic organisms (e.g. Cryptophyceans, Euglenoids). A linear mixed effects model identified abiotic factors, particularly temperature and river discharge, as significant predictors of the net aquatic metabolism and community respiration during flood conditions. Our results suggest that the role of the Ebro floodplain lakes as sources or sinks of C is complex and relative to the time scale investigated, depending strongly on the river discharge dynamics and the transport of limiting nutrients (phosphorus).     

The role of geomorphology in evaluating remediation options for floodplain wetlands: the case of Ramsar-listed Seekoeivlei,eastern South Africa

The range of benefits bestowed by wetlands is today increasingly recognized, and remediation of degraded wetlands is being carried out around the world. Many degraded wetlands are associated with river floodplains, and an essential requirement for their remediation planning is a comprehensive knowledge of the geomorphological functioning of the river channel and floodplain. Here, we review previous geomorphological investigations of the Ramsar-listed Seekoeivlei floodplain wetlands, Free State Province, South Africa, and demonstrate how the knowledge gained is playing a key role in evaluating remediation options that are needed following more than a century of direct and indirect human impacts. Faunal and floral changes, coupled with channel modifications, have altered the flow and sediment regime and initiated major changes to erosional and depositional patterns, including promoting rapid headward growth of a new channel and abandonment of a former channel. These changes have led to further management interventions, including installation of weirs and erosion control structures. In an ideal world, remediation would strive to return a wetland to its natural, pre-impact state but, in reality, other management goals have to be taken into consideration. In the case of Seekoeivlei, these include maintaining current habitat and biodiversity (this has the added advantage of promoting local tourism, especially bird watching), and using the wetlands for water quality enhancement. Attempts to return the wetlands to their pre-impact state (e.g. by removing exotic trees and erosion control structures) would in fact further reduce habitat and biodiversity, permanently in the case of some avian species, and for centuries in the case of some aquatic species, because of the very slow natural rates of channel and floodplain change. Alternative options will all require ongoing intervention, albeit of variable intensity, but in effect will mean that the wetland will never return to its pre-impact state. Remediation will thus create an essentially ‘artificial’ wetland complex that restores some of the ecological and hydrological functions but that is likely to remain very far from its natural geomorphic condition.     

Molecular biomarkers in the subsurface of the Salar Grande (Atacama,Chile) evaporitic deposits

Denitrification in riparian wetlands plays a major role in eliminating nitrate coming from agricultural watershed uplands before they reach river water. A new approach was developed for representing this process in the biogeochemical Riverstrahler model, using a single adjustable parameter representing the potential denitrification rate of wetland soils. Applied to the case of three watersheds with contrasting size, land-use and hydro-climatic regime, namely the Seine and the Loir rivers (France) and the Red River (Vietnam), this new model is able to capture the general level of nitrate concentrations as well as their seasonal variations everywhere over the drainage network. The nitrogen budgets calculated from the results show that riparian denitrification eliminates between 10 and 50% of the diffuse sources of nitrogen into the hydrosystem coming from soil nitrate leaching.     

The hydrochemical response of small and shallow floodplain water bodies to temporary surface water connections with the main river

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Response of wetland plant communities to inundation within floodplain landscapes

Summary Many floodplain wetlands in south‐eastern Australia have become isolated from the main river channel as a consequence of reduced high flows and associated flood events following river regulation. In the Central Murray region of south‐eastern Australia, many temporary wetlands would have received water once every five years or so, with large floods maintaining floodplain connectivity every decade, under natural conditions. Now, the River Murray is highly regulated and many of these wetland areas have not been flooded for periods of up to 30 years. Consequently, these wetlands are becoming degraded and the biodiversity of the area is in decline. From 2001–2003, 21 Black Box depression wetlands in the Central Murray region were each watered once. Plant communities in each wetland were monitored for changes in abundance (assessed as percentage cover) before and during the wetting and drying phases. Wetlands were watered during spring or early summer with the length of inundation ranging from 6 to 19 weeks. After watering, the percentage cover of native plant taxa and native plant functional groups in most wetlands increased. In general, there was a decrease in the percentage number of terrestrial plants present and an increase in the percentage cover of aquatic plants. Introduced species were a minor component. Although these wetlands are all located in the Central Murray region, individual wetlands developed plant communities that contained taxa specific to individual wetlands despite initial similarities. These results indicate that wetland plant biodiversity within the landscape can be promoted and maintained by ensuring there is a diversity of wetlands with varying flood regimes within the landscape.     

Water quality dynamics of oxbow lakes in young glacial landscape of NE Poland in relation to their hydrological connectivity

In this paper, the functioning of floodplain lakes was documented on the basis of water quality and hydrological data in a postglacial river floodplain representative of the temperate climatic zone. Nine oxbow lakes in the middle section of the River ?yna floodplain located in north-eastern Poland were investigated. Three groups of oxbow lakes distinguished on the basis of hydrological connectivity and retention time (lotic, semi-lotic and lentic) showed significant spatial and temporal differences in chemical parameters of water and matter cycling in relation to water table fluctuations, sediment character and aquatic plant diversity. Lotic habitats had parameters similar to river water, in particular to EC, main cation and anion concentrations. When the connection to a river is maintained, oxbow lakes prolong their existence due to multiple exchanges of matter. Very short-term water retention in lotic habitats is not favorable for sedimentation of such particles as Ca or SO₄, Na, K, Cl which are easily moved by river water. This is contrary to lentic (disconnected) water bodies, where retention time is incomparably longer and internal cycling limits ecosystem productivity. Disconnected oxbow lakes undergo the highest seasonal variations in nutrient availability related in summer to intensive development of free-floating phytocenoses that limit light and aeration conditions, whereas and in winter to long-term ice cover. The presented data indicate an important function of oxbow lakes that relies on the regulation of nutrient transfer towards rivers. The effectiveness of TIN withdrawal from lentic oxbow lakes is estimated as 75%, whereas and in other macroelements from 50% to 82%, when compared to the lotic type. The retention ability of natural riverine ecosystems should be considered in proper designs of created wetlands.     

Hydrogeomorphology Influences Soil Nitrogen and Phosphorus Mineralization in Floodplain Wetlands

Conceptual models of river–floodplain systems and biogeochemical theory predict that floodplain soil nitrogen (N) and phosphorus (P) mineralization should increase with hydrologic connectivity to the river and thus increase with distance downstream (longitudinal dimension) and in lower geomorphic units within the floodplain (lateral dimension). We measured rates of in situ soil net ammonification, nitrification, N, and P mineralization using monthly incubations of modified resin cores for a year in the forested floodplain wetlands of Difficult Run, a fifth order urban Piedmont river in Virginia, USA. Mineralization rates were then related to potentially controlling ecosystem attributes associated with hydrologic connectivity, soil characteristics, and vegetative inputs. Ammonification and P mineralization were greatest in the wet backswamps, nitrification was greatest in the dry levees, and net N mineralization was greatest in the intermediately wet toe-slopes. Nitrification also was greater in the headwater sites than downstream sites, whereas ammonification was greater in downstream sites. Annual net N mineralization increased with spatial gradients of greater ammonium loading to the soil surface associated with flooding, soil organic and nutrient content, and herbaceous nutrient inputs. Annual net P mineralization was associated negatively with soil pH and coarser soil texture, and positively with ammonium and phosphate loading to the soil surface associated with flooding. Within an intensively sampled low elevation flowpath at one site, sediment deposition during individual incubations stimulated mineralization of N and P. However, the amount of N and P mineralized in soil was substantially less than the amount deposited with sedimentation. In summary, greater inputs of nutrients and water and storage of soil nutrients along gradients of river–floodplain hydrologic connectivity increased floodplain soil nutrient mineralization rates.     

Flood regime,dam regulation and fish in the Upper Paraná River: effects on assemblage attributes,reproduction and recruitment

The flood regime is the most important force determining seasonality in neotropical rivers. In the Upper Paran River floodplain, it is the primary factor influencing biological processes. The aim of this paper is to summarize information on the influence of dam-controlled floods on some fish assemblage attributes, reproduction and recruitment in the Upper Paran River floodplain, providing preliminary guidelines for dam operation upstream. Fish were collected in different habitats of the Upper Paran River floodplain (river, channels and lagoons) in the period from 1986 to 2001. The high water period in the Paran River usually occurs from November/December to April/May. Annual variation in the hydrograph affects species with distinct life history strategies differently, and influences the composition and structure of fish assemblages. Large floods were associated with higher species richness. Frequencies of individuals with ripe and partially spent gonads, which indicate spawning, were higher during the period of increasing water level. Dependence on floods seems to be lowest in sedentary species that develop parental care, and highest in large migratory species that spawn in the upper stretches of the basin and use flooded areas as nurseries. Migratory fishes were favored by annual floods that lasted more than 75 days, with longer floods yielding larger populations. The occurrence of high water levels at the beginning of summer is fundamental to the spawning success of migratory species. However, the flood may be less important for recruitment of juveniles if it is of short duration. Dam operation upstream (releasing more water during the raining season) has potential to promote greater floods with appropriate duration improving recruitment, particularly for migratory species.     

The influence of leaf litter on zooplankton in floodplain wetlands: changes resulting from river regulation

1. The loss of input of leaf litter through clearing of riparian vegetation may result in significant changes to aquatic ecosystems. River red gums (Eucalyptus camaldulensis) surrounding floodplain wetlands in the Murray–Darling Basin, Australia, contribute large quantities of leaf litter, but the quality of this resource may change depending on the timing of inundation. 2. We used experimental mesocosms to test the hypotheses that zooplankton would have a greater abundance with an input of leaf litter and that fewer zooplankton would emerge from egg banks in cleared than forested wetlands. The experiment was carried out in summer/autumn and in spring to test a third hypothesis that zooplankton would respond to changes in the timing of wetland inundation as a result of river regulation. 3. In summer/autumn, leaf litter reduced zooplankton abundance by 89% at the beginning of the experiment through its influence on water quality. Only a few taxa (Polyarthra spp., Colurella spp. and the cladoceran Family Moinidae) responded positively to leaf litter when water quality improved later in the experiment, indicating a switch in the role of leaf litter from a non‐trophic to a trophic pathway. 4. In spring, microcrustaceans emerged in smaller numbers from sediment sourced from cleared compared to forested wetlands, reflecting different communities in these two wetland types and/or disturbances to the sediment that interfere with emergence. 5. Although leaf litter appears not to be an important resource for zooplankton in floodplain wetlands, riparian clearing may have lasting effects on future emerging zooplankton communities. Additionally, river regulation may have considerable impacts on the influence of leaf litter on zooplankton, which has implications for the management of floodplain river systems.     

Effects of sediment removal on nitrogen uptake by riparian plants in the higher floodplain of the Chikuma River, Japan

Riparian plants can use nitrogen (N) from soil and river water, but the use of river water N might be limited in higher floodplain environments of the Chikuma River. The purpose of this study is to reveal the relationship between N uptake by riparian plants and the floodplain topography (relative height and distance from a river channel). We examined the hypothesis that surface sediment removal from the higher floodplain increases river water N uptake by riparian plants by using a stable isotope analysis. The δ¹⁵N value of river water samples (ca. 8‰) were significantly higher than those of the soil extracts (ca. 3‰) in the study area. The δ¹⁵N value of riparian plants increased from +3.0‰ (standard deviation, SD ±2.1‰) before sediment removal to +9.6‰ (±2.1‰) after sediment removal, although there was no significant change in the δ¹⁵N value in N sources of soil and river water. The sediment removal enhanced frequency of flood disturbance, relative ground water level, and river water N uptake by riparian plants on the floodplain.     

Hydrologic and geomorphic considerations in restoration of river-floodplain connectivity in a highly altered river system,Lower Missouri River,USA

Planning for restoration of river-floodplain systems requires understanding how often and how much of a floodplain may be inundated, and how likely the floodplain is to retain the water once flooded. These factors depend fundamentally on hydrology and geomorphology of the channel and floodplain. We discuss application of an index of river-floodplain connectivity, the Land Capability Potential Index (LCPI), to regional-scale restoration planning along 600 km of the Lower Missouri River. The LCPI integrates modeled water-surface elevations, floodplain topography, and soils to index relative wetness of floodplain patches. Geomorphic adjustment of the Lower Missouri River to impoundment and channel engineering has altered the natural relations among hydrology, geomorphology, and floodplain soils, and has resulted in a regional upstream to downstream gradient in connectivity potential. As a result, flow-regime management is limited in its capacity to restore floodplain ecosystems. The LCPI provides a tool for identifying and mapping floodplain restoration potential, accounting for the geomorphic adjustment. Using simple criteria, we illustrate the utility of LCPI-like approaches in regional planning for restoration of plains cottonwood (Populus deltoides) communities, hydrologically connected floodplain wetlands, and seasonal floodplain wetlands.     

Hydrological variability, organic matter supply and denitrification in the Garonne River ecosystem

1. Groundwater nitrate contamination has become a worldwide problem as increasing amounts of nitrogen fertilisers are used in agriculture. Alluvial groundwater is uniquely juxtaposed between soils and streams. Hydrological connections among these subsystems regulate nutrient cycling. 2. We measured denitrification using an in situ acetylene‐block assay in a nitrate‐contaminated portion of the Garonne River catchment along a gradient of surface water–ground water mixing during high (snowmelt) and low flow. 3. During high flow (mid‐April to early June) the water table rose an average of 35 cm and river water penetrated the subsurface to a great extent in monitoring wells. Denitrification rates averaged 5.40 μgN₂O L^?1 min^?1 during the high flow period, nearly double the average rate (2.91 μgN₂O L^?1 min^?1) measured during base flow. This was driven by a strong increase in denitrification in groundwater under native riparian vegetation. Nitrate concentrations were significantly lower during high flow compared with base flow. Riparian patches had higher dissolved organic carbon concentrations that were more aromatic compared with the gravel bar patch closest to the river. 4. Multiple linear regression showed that the rate of denitrification was best predicted by the concentration of low molecular weight organic acids. These molecules are probably derived from decomposition of soil organic matter and are an important energy source for anaerobic respiratory processes like denitrification. The second best predictor was per cent surface water, reflecting higher denitrification rates during spring when hydrological connection between surface water and ground water was greatest. 5. Our results indicate that, while denitrification rates in Garonne River alluvium were spatially and temporally variable, denitrification was a significant NO₃ sink during transport from the NO₃‐contaminated floodplain to the river. DOC availability and river–floodplain connectivity were important factors influencing observed spatial and temporal patterns.     

Integrated stream and wetland restoration: A watershed approach to improved water quality on the landscape

Water quality in Upper Sandy Creek, a headwater stream for the Cape Fear River in the North Carolina Piedmont, is impaired due to high N and P concentrations, sediment load, and coliform bacteria. The creek and floodplain ecosystem had become dysfunctional due to the effects of altered storm water delivery following urban watershed development where the impervious surface reached nearly 30% in some sub-watersheds. At Duke University, an 8-ha Stream and Wetland Assessment Management Park (SWAMP) was created in the lower portion of the watershed to assess the cumulative effect of restoring multiple portions of stream and former adjacent wetlands, with specific goals of quantifying water quality improvements. To accomplish these goals, a three-phase stream/riparian floodplain restoration (600 m), storm water reservoir/wetland complex (1.6 ha) along with a surface flow treatment wetland (0.5 ha) was ecologically designed to increase the stream wetland connection, and restore groundwater wetland hydrology. The multi-phased restoration of Sandy Creek and adjacent wetlands resulted in functioning riparian hydrology, which reduced downstream water pulses, nutrients, coliform bacteria, sediment, and stream erosion. Storm water event nutrient budgets indicated a substantial attenuation of N and P within the SWAMP project. Most notably, (NO₂⁻ + NO₃⁻)-N loads were reduced by 64% and P loads were reduced by 28%. Sediment retention in the stormwater reservoir and riparian wetlands showed accretion rates of 1.8 cm year⁻¹ and 1.1 cm year⁻¹, respectively. Sediment retention totaled nearly 500 MT year⁻¹.