Erosion and sediment yield in the Atna river basin

Variability in suspended sediment transport and its relation to erosion processes in two different catchments within the Atna river basin are discussed on the basis of 14 years of data collection. The upper Atna catchment is a headwater system covering 157 km². Extensive glacifluvial deposits are the main sediment source of the river. Sediment transport in the upper Atna during 1988–2001 ranged from 79.4 t to 13,200 t. The extreme upper value was due to an extreme rainflood in 1996. Suspended sediment concentrations varied from less than 1.0 mg l^?1 to a maximum of 2023.8 mg l^?1. There was no correlation between water discharge and suspended sediment concentration. Despite a fairly constant volume of total runoff, sediment concentrations remained at a high level during the first years after extreme floods, and then decreased over several more years. The complicated pattern of short term and long term variations in suspended sediment concentration and load was explained in terms of channel changes and variations in exposure of the sedimentary deposits to fluvial erosion. The catchment of the lower Atna drains an area of 672 km². Concentrations of inorganic suspended sediments were found to vary between <1.0 and 897 mg l^?1, with only a weak correlation to water discharge. The suspended sediment transport per year ranged from a minimum value of 574 t in 1991 to 60,651 t per year in 1995, the extreme flood year. The mean annual transport for all the years was 6271 t. The sediment transported in the lower Atna is derived from the same types of sources as in the upper catchment, but the sediments are supplied from a larger area. Grain size distribution analyses indicate that the transported sediments in upper Atna have a sand content of 10 to 65% compared to 2–20% in lower Atna. The transport of particulate organic matter in the upper and lower Atna catchments amounted to 9.8% and 12.6% of the total load, respectively.     

Estimating sediment yield variation in a small forested upland catchment

A 14-month study of bedload and suspended sediment generation in three gauged subcatchments of a small coniferous forested upland drainage basin in the Southern Pennines of the United Kingdom revealed considerable variations in sediment yield (7–124 t km^–2 yr^–1). Clockwise hysteresis relationships between suspended sediment and discharge variables were found during storm runoff events at all three sites. Scatter in this relationship was found to be high, and as a consequence, estimates of suspended sediment transport obtained by regression analysis of the two variables during the period of study were found to be imprecise. It is proposed that such estimation procedures are unsuitable in headwater streams. Instead, a simple lumped conceptual model is proposed as an alternative framework for future predictive work in similar hydrologic regimes. Using discharge as the only input variable, the model has an areally distributed sediment store which may be accessed during storm flows. The model was calibrated using data from a wide range of fully monitored storms. Outputs from a 10-month run of the model compared well with depositional fluxes measured in sediment traps maintained concurrently in a reservoir into which the three streams drain.     

Freeze–thaw processes and intense rainfall: the one-two punch for high sediment and nutrient loads from mid-Atlantic watersheds

Large runoff, sediment, and nutrient exports from watersheds could occur due to individual extreme climate events or a combination of multiple hydrologic and meteorological conditions. Using high-frequency hydrologic, sediment, and turbidity data we show that freeze–thaw episodes followed by intense winter (February) rainstorms can export very high concentrations and loads of suspended sediment and particulate organic carbon (POC) and nitrogen (PN) from mid-Atlantic watersheds in the US. Peak suspended sediment (> 5000 mg L^?1), POC (> 250 mg L^?1) and PN (> 15 mg L^?1) concentrations at our 12 and 79 ha forested watersheds for the February rainfall-runoff events were highest on record and the fluxes were comparable to those measured for tropical storms. Similar responses were observed for turbidity values (> 400 FNU) at larger USGS-monitored watersheds. Much of the sediments and particulate nutrients likely originated from erosion of stream bank sediments and/or channel storage. Currently, there is considerable uncertainty about the contribution of these sources to nonpoint source pollution, particularly, in watersheds with large legacy sediment deposits. Future climate projections indicate increased intensification of storm events and increased variability of winter temperatures. Freeze–thaw cycles coupled with winter rain events could increase erosion and transport of streambank sediments with detrimental consequences for water quality and health of downstream aquatic ecosystems.     

Flow velocity retardation and sediment retention in two constructed wetland–ponds

Hydraulic properties of two constructed wetland–ponds in agricultural watersheds in southern Finland were examined by simulations with two-dimensional hydrodynamic and water quality transport models. Hydraulic efficiency was determined for the existing and hypothetical layouts of both wetlands to find out the effects of different design options. Suspended sediment retention in the wetlands was simulated with a two-dimensional model for sediment transport. Hydraulic efficiency was found to be highly improved by baffles that direct the main flow to optimally exploit the wetland acreage. Also, an elongated shape of wetland appeared beneficial; hydraulic efficiency was high regardless of the size or position of the inlet. As for suspended sediment retention, the wetland area in relation to its watershed proved to be an essential factor. According to water quality observations, the wetland which occupied 5% of its watershed area was capable of reducing the inflow of total suspended solids (TSS) concentrations during flood events by 43–72%, whereas the reduction varied between −7 and 5% in the other wetland with a corresponding ratio of 0.5%. Model simulations of the same flood events plausibly predicted the output TSS concentrations, even though with wider ranges of the reductions (26 to 74 and −13 to 43%, respectively).     

The use of turbidimeters in suspended sediment research

Accurate characterisation of the trend in suspended sediment concentration in streams throughout runoff events requires a sampling interval much shorter than the one hour typically used. For logistical reasons this is not usually feasible, so continuously recording turbidimeters offer a potential alternative. The variety of correlations and relationships between sediment concentration and turbidity reported in the literature is not surprising in view of the many confounding effects present in natural stream systems. Data from five sites in a small forested catchment indicated variability in the turbidity-suspended sediment concentration relationship, but improvements were obtained by considering the effects of very fine sediment and background water colour. Throughout runoff events variations in sediment properties, organic acids concentration and turbulence can occur. It is concluded that a good linear relationship between turbidity and suspended sediment concentration should not necessarily be expected and any observed hysteresis could actually help explain erosion and transport processes. The detail and continuity of data generated by turbidimeters provides the opportunity for greater understanding of storm sediment dynamics, however, calibration requires careful consideration of site characteristics.     

Case studies of variations in suspended matter transport in small catchments

Changes of water and suspended sediment composition during three single flood events were investigated in two small catchments in the Mosel region. In addition to suspended sediment characteristics (turbidity, loss on ignition, density, chlorophyll content), several different nutrients and heavy metals were determined in the dissolved and particulate phase. The flood events investigated were characterized by a single peaked hydrograph. In contrast suspended sediment concentrations and the other parameters showed more complex behaviour. The transport of suspended sediment was not only controlled by discharge magnitude. In the course of a flood event different suspended sediment sources are activated. Using the chemograph and the timing of samples collected during the hydrograph these suspended sediment sources can be identified. In addition to the remobilization of sediment and channel erosion, inputs of suspended solids from a sewage plant, road discharge, topsoil and interflow could be identified.     

The WEPP Model Application in a Small Watershed in the Loess Plateau

In the Loess Plateau, soil erosion has not only caused serious ecological and environmental problems but has also impacted downstream areas. Therefore, a model is needed to guide the comprehensive control of soil erosion. In this study, we introduced the WEPP model to simulate soil erosion both at the slope and watershed scales. Our analyses showed that: the simulated values at the slope scale were very close to the measured. However, both the runoff and soil erosion simulated values at the watershed scale were higher than the measured. At the slope scale, under different coverage, the simulated erosion was slightly higher than the measured. When the coverage is 40%, the simulated results of both runoff and erosion are the best. At the watershed scale, the actual annual runoff of the Liudaogou watershed is 83m³; sediment content is 0.097 t/m³, annual erosion sediment 8.057t and erosion intensity 0.288 t ha^-1 yr^-1. Both the simulated values of soil erosion and runoff are higher than the measured, especially the runoff. But the simulated erosion trend is relatively accurate after the farmland is returned to grassland. We concluded that the WEPP model can be used to establish a reasonable vegetation restoration model and guide the vegetation restoration of the Loess Plateau.     

Concentration and transport of dissolved and suspended substances in the Orinoco River

The Orinoco River, which is hydrologically unregulated and has a minimally disturbed watershed, was sampled quantitatively over a four-year interval. In conjunction with the sampling, a method was developed for quantifying statistical uncertainty in the estimates of annual transport. The discharge-weighted mean concentration of total suspended solids in the Orinoco River is 80 mg/l, which corresponds to total annual transport of 90 × 10⁶ t/y, or, expressed per unit of watershed area, 960 kg/ha/y, of which 96% is inorganic. The mean for dissolved solids is 34 mg/l, of which 25 mg/l is inorganic. The total transport of inorganic material, with a small allowance for bedload, is 128 × 10⁶ t/y, which corresponds to an erosion rate of 4 cm/1000 y. Concentrations of dissolved and suspended constituents derived from rock weathering are very low because of dilution from high runoff (1190 mm/y), coverage of the southern part of the drainage by shield rock, and minimal watershed disturbance. Seasonal patterns in dissolved and suspended constituents are repeated with a high degree of consistency from one year to the next. For most variables, relationships between transport and discharge are described adequately by a power function. There are three categories of response to changing discharge: purging (exponent > 1: soluble organic fractions and all particulate fractions), dilution (exponent 0–1: major ionic solids and silicon), and conservation (exponent < 0: nitrate, interannual). Variability across seasons and across years is highest for the particulate constituents, but within this group variability is lower for the organic than for the inorganic components. Major ions that originate primarily from the atmosphere have a higher seasonal variability than major ions that originate primarily from weathering. Potassium and soluble silicon have the lowest variabilities. Variability is much lower across years than across seasons for most constituents. Because of high runoff per unit area, the Orinoco drainage has a high specific transport of organic carbon (72 kg/ha/y, 6.8 × 10⁶ t/y, 1.6% of global river transport), even though the concentrations of organic carbon in the river are not exceptionally high (mean, 4.4 mg/l dissolved, 1.4 mg/l particulate). Concentrations of ammonium (35 μg/l as N) and of nitrate (80 μg/l as N) are high given the undisturbed nature of the watershed and the high amount of runoff. The high transport rate for total nitrogen (5.7 kg/ha/y, 0.54 × 10⁶ t/y, l.5% of global river transport) can be sustained only by high rates of nitrogen fixation within the watershed. Concentrations of soluble phosphorus are within the range expected for undisturbed river systems (20 μg/l), but concentrations of particulate phosphorus are low because the amounts of particulate matter are small and the phosphorus per unit weight of suspended matter is low. Phosphorus transport (0.75 kg/ha/y) can be accounted for easily by weathering of the parent material, even within the Guayana Shield, where weathering rates are lowest. Biological modification of nutrient and carbon fractions during transit along the main stem are minimal.     

Interpretation of sedimentation data measured in a former tidal channel Lake Volkerak

In Lake Volkerak, situated in the southwest of the Netherlands, downward settling fluxes are related to external inputs of suspended solids and wind action. The settling fluxes, measured using sediment traps, were 55 g (dw) m ^–2 d ^–1 on average. The ratio of metal concentration to scandium concentration was used to discriminate between external (polluted) suspended solids and internal (relatively clean) suspended solids. Generally, the contribution of the river suspended solids was small compared to that of resuspended material; the river-transported material was mainly deposited in the centre and to the east of the lake. The amount of material trapped increased substantially with increasing wind velocity.A simple model was used to interpretate the data. This model does not have a predictive capacity, but can be used to interpret and assess the significance of material retained in the sediment traps. Erosion was related to the wind velocity, using an empirical relationship between the orbital velocity of the wind-generated waves at the bottom and the wind velocity. The critical wind velocity for erosion to occur was estimated to be 5.5 m s^–1. The extremely high amounts retained in the sediment traps in shallow areas during storms emphasised the importance of these wind conditions for the transport of fine sediments.     

The Effect of Leaf Litter Cover on Surface Runoff and Soil Erosion in Northern China

The role of leaf litter in hydrological processes and soil erosion of forest ecosystems is poorly understood. A field experiment was conducted under simulated rainfall in runoff plots with a slope of 10%. Two common types of litter in North China (from Quercus variabilis, representing broadleaf litter, and Pinus tabulaeformis, representing needle leaf litter), four amounts of litter, and five rainfall intensities were tested. Results revealed that the litter reduced runoff and delayed the beginning of runoff, but significantly reduced soil loss (p<0.05). Average runoff yield was 29.5% and 31.3% less than bare-soil plot, and for Q. variabilis and P. tabulaeformis, respectively, and average sediment yield was 85.1% and 79.9% lower. Rainfall intensity significantly affected runoff (R = 0.99, p<0.05), and the efficiency in runoff reduction by litter decreased considerably. Runoff yield and the runoff coefficient increased dramatically by 72.9 and 5.4 times, respectively. The period of time before runoff appeared decreased approximately 96.7% when rainfall intensity increased from 5.7 to 75.6 mm h⁻¹. Broadleaf and needle leaf litter showed similarly relevant effects on runoff and soil erosion control, since no significant differences (p≤0.05) were observed in runoff and sediment variables between two litter-covered plots. In contrast, litter mass was probably not a main factor in determining runoff and sediment because a significant correlation was found only with sediment in Q. variabilis litter plot. Finally, runoff yield was significantly correlated (p<0.05) with sediment yield. These results suggest that the protective role of leaf litter in runoff and erosion processes was crucial, and both rainfall intensity and litter characteristics had an impact on these processes.     

极端降雨下黄土高原草被沟坡浅层滑坡特征及其对产流产沙的影响

植被恢复作为黄土高原防治水土流失的重要措施,但极端降雨诱发的浅层滑坡在植被恢复的沟坡上频繁发生,影响流域的产流产沙过程。基于野外原位模拟降雨试验,在60 mm/h降雨强度下,研究草被沟坡浅层滑坡发生特征及其发生前后的产流产沙差异。结果表明：（1）极端降雨所诱发的草被沟坡上的浅层滑坡深度为14-36 cm,与自然强降雨所导致的浅层滑坡深度相贴合,均是低于50 cm。（2）植被根系与土壤容重、孔隙度等土壤性质显著相关（P<0.05）,致使滑坡面上、下层土壤物理性质差异显著（P<0.05）。由于土壤性质的差异,在极端降雨下滑坡面上层土壤水分更快达到饱和（饱和度>90%）,导致浅层滑坡的发生。（3）草被坡面浅层滑坡后的径流与产沙均显著增大（P<0.05）。三个小区的平均径流率在滑坡后增大了4.0-13.1倍,其平均含沙量和产沙率在滑坡后分别增大了9.9-54.9倍和70-841倍。研究结果有助于加深了解植被沟坡的侵蚀产沙机理,并为浅层滑坡防治提供科学依据。     

Soil Organic Carbon Loss and Selective Transportation under Field Simulated Rainfall Events

The study on the lateral movement of soil organic carbon (SOC) during soil erosion can improve the understanding of global carbon budget. Simulated rainfall experiments on small field plots were conducted to investigate the SOC lateral movement under different rainfall intensities and tillage practices. Two rainfall intensities (High intensity (HI) and Low intensity (LI)) and two tillage practices (No tillage (NT) and Conventional tillage (CT)) were maintained on three plots (2 m width × 5 m length): HI-NT, LI-NT and LI-CT. The rainfall lasted 60 minutes after the runoff generated, the sediment yield and runoff volume were measured and sampled at 6-min intervals. SOC concentration of sediment and runoff as well as the sediment particle size distribution were measured. The results showed that most of the eroded organic carbon (OC) was lost in form of sediment-bound organic carbon in all events. The amount of lost SOC in LI-NT event was 12.76 times greater than that in LI-CT event, whereas this measure in HI-NT event was 3.25 times greater than that in LI-NT event. These results suggest that conventional tillage as well as lower rainfall intensity can reduce the amount of lost SOC during short-term soil erosion. Meanwhile, the eroded sediment in all events was enriched in OC, and higher enrichment ratio of OC (ERoc) in sediment was observed in LI events than that in HI event, whereas similar ERoc curves were found in LI-CT and LI-NT events. Furthermore, significant correlations between ERoc and different size sediment particles were only observed in HI-NT event. This indicates that the enrichment of OC is dependent on the erosion process, and the specific enrichment mechanisms with respect to different erosion processes should be studied in future.     

黄土高原景观格局与水土流失关系研究

采用DCCA排序法对黄土高原腹地泾河流域12个子流域的景观格局与流域水土流失关系进行了定量分析.结果表明,DCCA排序的前4轴分别与农业用地比率、景观多样性指数、森林比率显著相关.各子流域的水土流失特征具有明显的梯度变异.在森林比率占65%的三水河子流域,景观相对简单、多样性低,流域年径流量大、输沙小、含沙量低,径流相对稳定;随着森林比率减小,农业用地比率增大,景观多样性升高,产流系数增高,径流深度、输沙量和含沙量增大;在森林比率很低、农业用地53.41%的洪河子流域,景观格局复杂、多样性较高,河流含沙量高、输沙率大,月输沙和径流变异极大;在农业用地比率减小,其他景观类型比率增大,景观相对简单的环江上、下游子流域,输沙量和含沙量减小,但输沙和径流的年际变化极大.排序分析结果较清晰地解释了黄土高原典型地区水土流失特征沿景观梯度的变化规律.     

极端降水条件下延河水沙特征对比分析及其影响因素

为探究延河流域在开展水土保持工程前后极端降水条件下水沙特征变化情况,采用统计学方法对比分析了延河流域1977年和2013年7月两次极端降水条件下的水沙特征变化情况。结果表明:1977年7月极端暴雨具有降雨强度大和降雨量峰值大、降雨强度空间分布极不均匀的特征;2013年7月极端暴雨具有降雨总量和时段降雨量大、暴雨频率高、降雨强度空间分布较均匀的特征。2013年7月洪水洪峰流量、洪水总径流量、洪峰含沙量等特征值较1977年7月显著减小,输沙量随径流量的减小而显著减小。1977年7月洪水表现为陡涨陡落,洪水历时较短;2013年7月洪水表现为缓涨缓落,洪水历时明显延长。与1977年相比,2013年泥沙颗粒明显细化。该研究表明1990年代以来水土保持高水平的规模化治理改变了流域产、汇流的下垫面条件,是导致1977年和2013年7月极端降水条件下的水沙特征表现迥异的主要原因。该研究为应对极端降水引发的洪灾和防治水土流失提供可靠的科学理论依据。     

西北干旱区气候和土地利用变化对水沙运移的影响——以小南川流域为例

认识区域水沙运移规律及其对气候和土地利用变化的响应能够为水土流失防治提供理论依据,是水土资源综合开发的重要前提.本研究以1963-2013年逐月实测气象、径流和泥沙资料为基础,结合20世纪80年代和2000年土地利用数据和归一化植被指数(NDVI)数据,采用Mann-Kendall趋势分析和突变检验方法,系统分析了西北干旱区典型小流域--小南川流域的气候和水沙长期变化特征,并识别了研究区土地利用及植被覆盖度变化特征.在对单要素变化充分解析的基础上,利用多元线性回归等方法,定量探讨了气候和土地利用变化对小南川流域水沙运移的影响机制,并明确了关键作用因子.结果表明: 小南川流域气温向两极化发展,降水量逐渐增加,总体气候变化趋势朝向暖湿方向,极端气候事件发生频率增加,且在20世纪90年代发生突变后,其变化速度和程度均进一步加剧.自20世纪80年代以来,随着经济社会发展,流域内耕地和城镇扩张,林地增加,自然生态环境向良性发展.在土地利用和植被覆盖度变化的主导驱动作用下,流域径流量和输沙量分别以1.7×10⁶ m³·(10 a)^-1和1.5×10⁸ kg·(10 a)^-1的平均速率呈减少趋势.定量化研究结果揭示了植被覆盖度和月平均最高气温是影响该区径流变化的最关键因子,而植被覆盖度和日最大降水量是影响输沙变化的最关键因子.在当前气候变化背景下,生态修复是防止干旱区流域水土流失的最有效途径之一.     

Release of metals from polluted sediments in a shallow lake: quantifying resuspension

The contribution of erosion of bed sediment to the load of metals leaving Lake Ketelmeer, a shallow lake in the Netherlands fed by the IJssel branch of the River Rhine, is reported. Transport of suspended matter and associated trace metals was measured using both centrifuges and sediment traps at several locations in the lake. Mass balances of suspended matter and heavy metals were calculated using data from these field measurements.Metal/scandium-ratios were used to identify the source of the suspended matter in the lake. Since the bed sediment is more polluted than the suspended sediment entering the lake, higher metal/scandium-ratios were found for bottom sediment in the lake compared with those for suspended matter entering the lake from the River IJssel. Using the metal/scadium-ratio in suspended matter from the lake, it was calculated that bottom sediments made up 43% of the suspended matter leaving the lake. This implies an erosion flux of bottom sediment of 16 g m^–2 d^–1. For cadmium, mercury, chromium and zinc, this erosion process accounts for more than 50% of the pollutant load leaving Lake Ketelmeer and entering Lake IJsselmeer.     

Do we know enough about controlling sediment to mitigate damage to stream ecosystems?

Stream and river ecosystems have suffered extensive degradation, and billions are expended annually on restoration efforts. However, few of these projects are monitored, and restoration effectiveness is often unknown. Consequently, there is a poor scientific foundation for restoration designs. Since many stream restoration efforts are at least partially targeted at controlling erosion of channel banks and beds, the effects of a large-scale, long-term stream erosion control effort in six Mississippi watersheds was assessed using 10–16 years of suspended sediment and water discharge records. Flow-adjusted suspended sediment concentrations showed no trends in five of the watersheds and a slight downward trend in one watershed, which was treated with small reservoirs as well as bed and bank erosion protection. Results indicate the inability of orthodox stream management structures (weirs and bank protection) to reduce watershed sediment yield and the need for a stronger scientific basis for stream restoration.     

Characterising the fine sediment budget of a reach of the River Swale,Yorkshire, U.K. during the 1994 to 1995 winter season

Suspended sediment budget dynamics for a 55 km reach of the lowland River Swale, Yorkshire, U.K. are investigated for the period October 1994 to June 1995. Particular attention is paid to 11 storm events occurring between October 1994 and April 1995. Each of these storms produced significant suspended sediment transport. Variations in sediment dynamics, for example suspended sediment concentrations, hysteresis patterns and storm peak lag times through events and between the upstream and downstream ends of the reach are examined. Net sediment loss from the reach occurred during the extremely wet four month winter period from December 1994 to April 1995. Patterns of reach sediment storage are concluded to represent a combination of channel bed erosion and/or deposition, bank erosion and floodplain deposition. The implications of these patterns for sediment modelling are discussed.     

Biostabilization and Transport of Cohesive Sediment Deposits in the Three Gorges Reservoir

Cohesive sediment deposits in the Three Gorges Reservoir, China, were used to investigate physical and geochemical properties, biofilm mass, and erosion and deposition characteristics. Biofilm cultivation was performed in a recirculating flume for three different periods (5, 10 and 15 days) under ambient temperature and with sufficient nutrients supply. Three groups of size-fractionated sediment were sequentially used, including 0–0.02 mm, 0.02–0.05 mm and 0.05–0.10 mm. Desired conditions for erosion and deposition were designed by managing high bed shear stress at the narrow part of upstream flume and low shear stress at the wide part of downstream flume. Biostabilization and transport characteristics of the biofilm coated sediment (bio-sediment) were strongly influenced by the cultivation period, and the results were compared with clean sediment. The bio-sediment was more resistant to erosion, and the mean shear stress was increased by factors of 2.65, 2.73 and 5.01 for sediment with 5, 10 and 15 days of biofilm growth compared with clean sediment, resulting in less sediment being eroded from the bed. Simultaneously, the settling velocity was smaller for bio-sediment due to higher organic content and porosity (i.e., lower density). Additionally, there was a smaller probability of deposition for sediment with a longer cultivation period after erosion, resulting in more retention time in aquatic systems. These results will benefit water management in natural rivers.     

Seasonal benthic nitrogen cycling in a temperate shelf sea: the Celtic Sea

Spring runoff often comprises the majority of annual discharge and riverine phosphorus (P) export due to sustained high flow, and the magnitude of spring runoff can be a strong predictor of receiving water summer harmful algal bloom severity. Yet the loading of reactive forms of P during this time period remains poorly-characterized in time, space and geochemical partitioning. Here, we explore the hypothesis that riverine dissolved and suspended sediment P loads during spring runoff have a particularly high proportion of potentially reactive species due to unique hydrologic pathways and P association with iron (Fe).The concentration, distribution and temporal dynamics of dissolved P (DP), dissolved and colloidal Fe, and redox sensitive suspended sediment P (RSP) and Fe during spring runoff and summer storms were compared in forested and agricultural catchments of the same watershed. The dominant carrier of RSP was Fe (oxy)hydroxides across land cover and season, but Fe (oxy)hydroxide particles and colloids in agricultural catchments were strongly enriched in RSP and DP during spring runoff and summer storms, particularly at the onset of snowmelt. In 2014, 83% of DP and 74% of RSP were delivered to Missisquoi Bay during spring runoff. Suspended sediment was significantly more redox sensitive than typically input to limnological models, suggesting that the reactivity of this load may be systematically underestimated. Changes in the timing, provenance and severity of spring runoff associated with climate or land cover change will have dramatic impacts on total riverine P loads and their potential reactivity in receiving water ecosystems.