Artificial Subsurface Drainage Research Articles

Nutrient losses from subsurface drainage systems in Latvia

Artificial subsurface drainage systems are a common water management practice to remove excess water from agricultural land in the Baltic and Nordic countries. Unfortunately, these systems also serve as nutrient transport pathways from agricultural fields to downstream waterbodies. The objective of this study was to determine the status of subsurface drainage water in the context of implementation of the European Union (EU) Water Framework Directive (WFD) and EU Nitrate Directive (ND), to investigate the impact of hydrology and mineral fertilizer application on nutrient losses through subsurface drainage systems and to evaluate the possible effects of climate change on drainage and nutrient loss. This research was conducted from 1995 through 2013 at the agricultural run-off–monitoring sites in Berze and Mellupite. Continuous-flow measurement data and composite water samples were collected on a monthly basis for assessment of total nitrogen (TN), nitrate–nitrogen (NO3–N) and total phosphorus (TP) in drainage water. Results from the study indicated that the mean annual NO3–N concentration was slightly below the threshold level defined by ND, while TN concentrations exceeded the threshold level for good chemical status of water according to WFD. Differences in TN losses were mainly driven by the hydrologic behaviour at the study sites rather than by mineral fertilizer application rates, whereas TP losses under similar application rates were affected by open inlets for surface water accumulation. The comparison of meteorological data for the research period (1995–2013) with the long-term mean (1950–1994) showed a pronounced evidence of climate change. The mean annual precipitation amount has increased at both Berze and Mellupite monitoring sites by 36 mm and 42 mm, respectively, compared to the long-term mean for 1950–1994. Meanwhile, the mean annual temperature during the research period was 7.3°C for Berze and 6.4°C for Mellupite, which is 1.4°C and 0.6°C warmer than long-term mean.

Characterizing phosphorus dynamics in tile-drained agricultural fields of eastern Wisconsin

Summary Artificial subsurface drainage provides an avenue for the rapid transfer of phosphorus (P) from agricultural fields to surface waters. This is of particular interest in eastern Wisconsin, where there is a concentrated population of dairy farms and high clay content soils prone to macropore development. Through collaboration with private landowners, surface and tile drainage was measured and analyzed for dissolved reactive P (DRP) and total P (TP) losses at four field sites in eastern Wisconsin between 2005 and 2009. These sites, which received frequent manure applications, represent a range of crop management practices which include: two chisel plowed corn fields (CP1, CP2), a no-till corn–soybean field (NT), and a grazed pasture (GP). Subsurface drainage was the dominant pathway of water loss at each site accounting for 66–96% of total water discharge. Average annual flow-weighted (FW) TP concentrations were 0.88, 0.57, 0.21, and 1.32 mg L −1 for sites CP1, CP2, NT, and GP, respectively. Low TP concentrations at the NT site were due to tile drain interception of groundwater flow where large volumes of tile drainage water diluted the FW-TP concentrations. Subsurface pathways contributed between 17% and 41% of the TP loss across sites. On a drainage event basis, total drainage explained between 36% and 72% of the event DRP loads across CP1, CP2, and GP; there was no relationship between event drainflow and event DRP load at the NT site. Manure applications did not consistently increase P concentrations in drainflow, but annual FW-P concentrations were greater in years receiving manure applications compared to years without manure application. Based on these field measures, P losses from tile drainage must be integrated into field level P budgets and P loss calculations on heavily manured soils, while also acknowledging the unique drainage patterns observed in eastern Wisconsin.

Cover crops in the upper midwestern United States: Simulated effect on nitrate leaching with artificial drainage

A fall-planted winter cover crop is an agricultural management practice with multiple benefits that may include reducing nitrate (NO₃) losses from artificial drained agricultural fields. While the practice is commonly used in the southern and eastern United States, little is known about its efficacy in midwestern states where winters are longer and colder, and artificial subsurface drainage is widely used in corn–soybean systems (<i>Zea mays</i> L.–<i>Glycine max</i> L.). We used a field-tested version of the Root Zone Water Quality Model (RZWQM) to simulate the adoption of cereal rye (<i>Secale cereale</i> L.) as a winter cover crop and estimate its impact on NO₃ losses from drained fields at 41 sites across the Midwest from 1961 to 2005. The average annual nitrogen (N) loss reduction from adding winter rye ranged from 11.7 to 31.8 kg N ha⁻¹ (10.4 to 28.4 lb N ac⁻¹) among four simulated systems. One of the simulated treatments was winter rye overseeded (aerial seeded) into a no-till corn–soybean rotation at simulated main crop maturity (CC2). On average, this treatment reduced simulated N loss in drainage by 20.1 kg N ha⁻¹ (17.9 lb N ac⁻¹) over the sites compared to systems without winter rye (NCC2), from 47.3 to 27.2 kg N ha⁻¹ (42.2 to 24.3 lb N ac⁻¹). Adding spring tillage to this treatment and killing the rye earlier (CC3) reduced simulated N loss from 57.3 (NCC3) to 34.4 kg N ha⁻¹ (30.7 lb N ac⁻¹). Replacing the corn–soybean rotation with continuous corn and spring tillage reduced simulated N loss from 106 (NCC4) to 74.2 kg N ha⁻¹ (CC4) (94.6 to 66.2 lb N ac⁻¹). Adding a winter rye cover crop reduced N loss more in the continuous corn system despite earlier spring termination of the winter rye and slightly less N uptake by the rye possibly because of more denitrification. Regression analysis of the RZWQM variables from these sites showed that temperature and precipitation during winter rye growth, N fertilizer application rates to corn, and simulated corn yield account for greater than 95% of the simulated site-to-site variability in NO₃ loss reductions in tile flow due to winter rye. Our results suggest that on average winter rye can reduce N loss in drainage 42.5% across the Midwest. Greater N loss reductions were estimated from adding winter rye at sites with warmer temperatures and less precipitation because of more cover crop growth and more soil N available for cover crop uptake.

Reconnecting tile drainage to riparian buffer hydrology for enhanced nitrate removal.

Riparian buffers are a proven practice for removing NO from overland flow and shallow groundwater. However, in landscapes with artificial subsurface (tile) drainage, most of the subsurface flow leaving fields is passed through the buffers in drainage pipes, leaving little opportunity for NO removal. We investigated the feasibility of re-routing a fraction of field tile drainage as subsurface flow through a riparian buffer for increasing NO removal. We intercepted an existing field tile outlet draining a 10.1-ha area of a row-cropped field in central Iowa and re-routed a fraction of the discharge as subsurface flow along 335 m of an existing riparian buffer. Tile drainage from the field was infiltrated through a perforated pipe installed 75 cm below the surface by maintaining a constant head in the pipe at a control box installed in-line with the existing field outlet. During 2 yr, >18,000 m (55%) of the total flow from the tile outlet was redirected as infiltration within the riparian buffer. The redirected water seeped through the 60-m-wide buffer, raising the water table approximately 35 cm. The redirected tile flow contained 228 kg of NO. On the basis of the strong decrease in NO concentrations within the shallow groundwater across the buffer, we hypothesize that the NO did not enter the stream but was removed within the buffer by plant uptake, microbial immobilization, or denitrification. Redirecting tile drainage as subsurface flow through a riparian buffer increased its NO removal benefit and is a promising management practice to improve surface water quality within tile-drained landscapes.

Homogenization of spatial patterns of hydrologic response in artificially drained agricultural catchments

AbstractAnthropogenic modifications to the landscape, with agricultural activities being a primary driver, have resulted in significant alterations to the hydrologic cycle. Artificial drainage, including surface and subsurface drainage (tile drains), is one of the most extensive manipulations in agricultural landscapes and thus is expected to provide a distinct signature of anthropogenic modification. This study adopts a data synthesis approach in an effort to characterize the signature of artificial subsurface drainage. Daily discharge data from 24 basins across the state of Iowa, which encapsulate a range of anthropogenic modifications, are assessed using a variety of flow metrics. Results indicate that the presence of artificial subsurface drainage leads to a homogenization of landscape hydrologic response. Non‐tiled watersheds exhibit a decrease in the area‐normalized peak discharge and an increase in the baseflow ratio (baseflow/streamflow) with increases in the spatial scale, while scale invariance is apparent in tiled basins. Within‐basin variability in hydrograph recession coefficients also appears to decrease with increases in the proportion of the catchment that is artificially drained. Finally, the differences between tiled and non‐tiled landscapes disappear at scales greater than approximately 2200 km2, indicating that this may be a threshold scale for studying the effects of tile drainage. This decrease in within‐basin variability and the scale invariance of hydrologic metrics in artificially drained watersheds are attributed to the creation of a bypass flow hydrologic pathway that bypasses the complexity of the catchment travel paths. Spatial homogeneity in responses implies that it may be possible to develop more parsimonious hydrologic models for these regions. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Impact of artificial subsurface drainage on groundwater travel times and baseflow discharge in an agricultural watershed, Iowa (USA)

AbstractPollutant delivery through artificial subsurface drainage networks to streams is an important transport mechanism, yet the impact of drainage tiles on groundwater hydrology at the watershed scale has not been well documented. In this study, we developed a two‐dimensional, steady‐state groundwater flow model for a representative Iowa agricultural watershed to simulate the impact of tile drainage density and incision depth on groundwater travel times and proportion of baseflow contributed by tile drains. Varying tile drainage density from 0 to 0.0038 m−1, while maintaining a constant tile incision depth at 1.2 m, resulted in the mean groundwater travel time to decrease exponentially from 40 years to 19 years and increased the tile contribution to baseflow from 0% to an upper bound of 37%. In contrast, varying tile depths from 0.3 to 2.7 m, while maintaining a constant tile drainage density of 0.0038 m−1, caused mean travel times to decrease linearly from 22 to 18 years and increased the tile contribution to baseflow from 30% to 54% in a near‐linear manner. The decrease in the mean travel time was attributed to decrease in the saturated thickness of the aquifer with increasing drainage density and incision depth. Study results indicate that tile drainage affects fundamental watershed characteristics and should be taken into consideration when evaluating water and nitrate export from agricultural regions. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Nitrate, Phosphate, and Ammonium Loads at Subsurface Drains: Agroecosystems and Nitrogen Management

Artificial subsurface drainage in cropland creates pathways for nutrient movement into surface water; quantification of the relative impacts of common and theoretically improved management systems on these nutrient losses remains incomplete. This study was conducted to assess diverse management effects on long-term patterns (1998-2006) of NO, NH, and PO loads (). We monitored water flow and nutrient concentrations at subsurface drains in lysimeter plots planted to continuous corn ( L.) (CC), both phases of corn-soybean [ (L.) Merr.] rotations (corn, CS; soybean, SC), and restored prairie grass (PG). Corn plots were fertilized with preplant or sidedress urea-NHNO (UAN) or liquid swine manure injected in the fall (FM) or spring (SM). Restored PG reduced NO eightfold compared with fields receiving UAN (2.5 vs. 19.9 kg N ha yr; < 0.001), yet varying UAN application rates and timings did not affect NO across all CCUANs and CSUANs. The NO from CCFM (33.3 kg N ha yr) were substantially higher than for all other cropped fields including CCSM (average 19.8 kg N ha yr, < 0.001). With respect to NH and PO, only manured soils recorded high but episodic losses in certain years. Compared with the average of all other treatments, CCSM increased NH in the spring of 1999 (217 vs. 680 g N ha yr), while CCFM raised PO in the winter of 2005 (23 vs. 441 g P ha yr). Our results demonstrate that fall manuring increased nutrient losses in subsurface-drained cropland, and hence this practice should be redesigned for improvement or discouraged.

Cover crop effects on nitrogen load in tile drainage from Walnut Creek Iowa using root zone water quality (RZWQ) model

Abstract Studies quantifying winter annual cover crop effects on water quality are mostly limited to short-term studies at the plot scale. Long-term studies scaling-up water quality effects of cover crops to the watershed scale provide more integrated spatial responses from the landscape. The objective of this research was to quantify N loads from artificial subsurface drainage (tile drains) in a subbasin of the Walnut Creek, Iowa (Story county) watershed using the hybrid RZWQ-DSSAT model for a maize ( Zea mays L.)-soybean [ Glycine max (L.) Merr.] and maize–maize–soybean rotations in all phases with and without a winter wheat ( Triticum aestivum L.) cover crop during a 25-year period from 1981 to 2005. Simulated cover crop dry matter (DM) and N uptake averaged 1854 and 36 kg ha −1 in the spring in the maize–soybean phase of the 2-year rotation and 1895 and 36 kg ha −1 in the soybean–maize phase during 1981–2005. In the 3-year rotation, cover crop DM and N uptake averaged 2047 and 44 kg ha −1 in the maize–maize–soybean phase, 2039 and 43 kg ha −1 in the soybean–maize–maize phase, and 1963 and 43 kg ha −1 in the maize–soybean–maize phase during the same period. Annual N loads to tile drains averaged 29 kg ha −1 in the maize–soybean phase and 25 kg ha −1 in the soybean–maize phase compared to 21 and 20 kg ha −1 in the same phases with a cover crop. In the 3-year rotation, annual N loads averaged 46, 43, and 45 kg ha −1 in each phase of the rotation without a cover crop and 37, 35, and 35 kg ha −1 with a cover crop. These results indicate using a winter annual cover crop can reduce annual N loads to tile drains 20–28% in the 2-year rotation and 19–22% in the 3-year rotation at the watershed subbasin scale over a 25-year period.

Drainage water management for water quality protection

L and drainage has been central to the development of North America since colonial times, with the first organized drainage efforts occurring as early as the 1600s (Evans et al. 1996). Drainage has been encouraged to improve public highways, reduce public health risks, promote increased crop yield and reduced yield variability, reduce surface runoff and erosion, and increase land value. Agricultural drainage includes artificial subsurface drainage and surface drainage. Most agricultural producers improve the drainage on their land for better trafficability, to enhance field conditions, to facilitate timely planting and harvesting operations, and to help decrease crop damage from saturated soil and standing water during the growing season. Agricultural drainage improvement also decreases year-to-year variability in crop yield, ensuring consistent production. Increasingly, agricultural drainage is being targeted as a conduit for pollution, particularly nutrient pollution (Needelman et al. 2007). Considerable resistance exists in some regions to the expansion of drainage systems despite their importance to food production, with up to 50% of the cropland in some states under artificial drainage. However, because drainage ditches and subsurface drainage systems convert diffuse flows from the landscape into concentrated flows, they also provide opportunities for precision conservation, the targeting of specific practices to…

Dissolved Organic Carbon Losses from Tile Drained Agroecosystems

Artificial subsurface drainage is commonly used in midwestern agriculture and drainage losses of dissolved organic carbon (DOC) from such systems are an under-quantified portion of the terrestrial carbon (C) cycle. The objectives of this study were to determine the effect of common agricultural management practices on DOC losses from subsurface tile drains and to assess patterns of loss as a function of year, time of year, and drainflow. Daily drainflow was collected across six water years (1999-2004) from a restored prairie grass system and cropping systems which include continuous corn (Zea mays L.) and corn-soybean [Glycine max (L.) Merr.] rotations fertilized with urea-ammonium-nitrate (UAN) or swine (Sus scrofa) manure lagoon effluent. The DOC concentrations in tile drainflow were low, typically <2 mg L(-1). Yearly DOC losses, which ranged from 1.78 to 8.61 kg ha(-1), were not affected by management practices and were small compared to organic C inputs. Spring application of lagoon effluent increased yearly flow-weighted (FW)-DOC concentrations relative to other cropping systems in three of the years and increased monthly FW-DOC concentrations when drainflow occurred within 1 mo of application. Drainflow was significantly and positively correlated with DOC loss. Drainflow also affected DOC concentrations as greater 6-yr cumulative drainflow was associated with lower 6-yr FW-DOC concentrations and greater daily drainflow was associated with higher daily DOC concentrations. Our results indicate that lagoon effluent application and fertilizer N rates do not affect long-term losses of DOC from tile drains and that drainflow is the main driver of DOC losses.

Water Balance Investigation of Drainage Water Management in Non-Weighing Lysimeters

Artificial subsurface drainage systems are often used throughout the upper Midwest to remove excess precipitation and improve crop production. However, these drainage systems export nitrate-nitrogen (NO3-N) to downstream water resources. Management practices are needed to reduce this export of NO3-N with subsurface drainage water. One such practice being considered is the use of drainage water management where subsurface water is held in the soil profile during portions of the year. Previous research has shown that drainage water management has potential to reduce subsurface drainage volume but there is still a need to understand the performance of the practice and the pathways of water flow under varying conditions. The objectives of this study, therefore, were to quantify the pathways of water movement for conventional or free drainage (FD) and drainage water management (DWM) during the growing season. In this study, six non-weighing lysimeters (0.92 2.30 m) with a depth of 120 cm were monitored over a 3-yr period under natural and simulated rainfall conditions. The objectives were performed to measure the effects of drainage water management (DWM) on surface runoff, subsurface drainage, and crop yield. The in-season data from natural rainfall conditions showed that DWM reduced subsurface drainage by approximately 14%. The simulated rainfall data showed that DWM increased surface runoff by 54% when the water table was established at 90 cm below the soil surface, and by 87% when the water table was established at 60 cm below the soil surface. Overall DWM was found to have the potential to reduce subsurface drainage but there is the potential that at least a portion of this reduction may be reflected in an increase in surface runoff.

Soil Drainage as an Active Agent of Recent Soil Evolution: A Review

While research on pedogenesis mainly focuses on long-term soil formation and most often neglects recent soil evolution in response to human practices or climate changes, this article reviews the impact of artificial subsurface drainage on soil evolution. Artificial drainage is considered as an example of the impact of recent changes in water fluxes on soil evolution over time scales of decades to a century. Results from various classical studies on artificial drainage including hydrological and environmental studies are reviewed and collated with rare studies dealing explicitly with soil morphology changes, in response to artificial drainage. We deduce that soil should react to the perturbations associated with subsurface drainage over time scales that do not exceeding a few decades. Subsurface drainage decreases the intensity of erosion and must i) increase the intensity of the lixiviation and eluviation processes, ii) affect iron and manganese dynamics, and iii) induce heterogeneities in soil evolution at the ten meter scale. Such recent soil evolutions can no longer be neglected as they are mostly irreversible and will probably have unknown, but expectable, feedbacks on crucial soil functions such as the sequestration of soil organic matter or the water available capacity.

Detecting subsurface drainage systems and estimating drain spacing in intensively managed agricultural landscapes

Detailed location maps of tile drains in the Midwestern United States are generally not available, as the tile lines in these areas were laid more than 75 years ago. The objective of this study is to map individual tile drains and estimate drain spacing using a combination of GIS-based analysis of land cover, soil and topography data, and analysis of high resolution aerial photographs to within the Hoagland watershed in west-central Indiana. A decision tree classifier model was used to classify the watershed into potentially drained and undrained areas using land cover, soil drainage class, and surface slope data sets. After masking out the potential undrained areas from the aerial image, image processing techniques such as the first-difference horizontal and vertical edge enhance filters, and density slice classification were used to create a detailed tile location map of the watershed. Drain spacings in different parts of the watershed were estimated from the watershed tile line map. The decision tree identified 79% of the watershed as potential tile drained area while the image processing techniques predicted artificial subsurface drainage in approximately 50% of the Hoagland watershed. Drain spacing inferred from classified aerial image vary between 17 and 80 m. Comparison of estimated tile drained areas from aerial image analysis shows a close agreement with estimated tile drained areas from previous studies (50% versus 46% drained area) which were based on GIS analysis and National Resource Inventory survey. Due to lack of sufficient field data, the results from this analysis could not be validated with observed tile line locations. In general, the techniques used for mapping tile lines gave reasonable results and are useful to detect drainage extent from aerial image in large areas. These techniques, however, do not yield precise maps of the systems for individual fields and may not accurately estimate the extent of tile drainage in the presence of crop residue in agricultural fields and/or existence of other spatial features with similar spectral response as tile drains.

Assessment of the Iowa River's South Fork watershed: Part 1. Water quality

Iowa's South Fork watershed is dominated by corn (Zea mays L.) and soybean (Glycine max L. (Merr.)) rotations, and animal feeding operations are common. Artificial subsurface (tile) drainage is extensive; hydric soils cover 54% of the watershed. During spring and early summer, NO 3 -N concentrations in tile and stream discharge often exceed 20 mg L -1 . Total N loads during 2002 to 2005 ranged from 16 to 26 kg NO 3 -N ha -1 y -1 (14 to 23 lb ac -1 yr -1 ). Nitrate concentrations increased linearly with log baseflow, effectively a surrogate measure of tile discharge. Phosphorus loads were only 0.4 to 0.7 kg P ha -1 y -1 (0.4 to 0.6 lb ac -1 yr -1 ), but concentrations commonly exceeded 0.1 mg L -1 , a eutrophica- tion-risk threshold. Mean E. coli populations in the stream exceeded 500 cells 100 ml -1 during summer. Statistical comparison of actual nitrate records with independent records generated using regression equations provided modeling efficiencies of 0.91 or less, suggesting perfor- mance targets for watershed model validation. Tile drainage is more important in transport of nitrate and dissolved phosphorus than E. coli. Variations in nitrate, phosphorus, and E. coli are uniquely timed, highlighting the complexity of integrated water quality assessments.

Effects of subsurface drainage tiles on streamflow in Iowa agricultural watersheds: Exploratory hydrograph analysis

AbstractFlow from artificial subsurface (tile) drainage systems may be contributing to increasing baseflow in Midwestern rivers and increased losses of nitrate‐nitrogen. Standard hydrograph analysis techniques were applied to model simulation output and field monitoring from tile‐drained landscapes to explore how flow from drainage tiles affects stream baseflow and streamflow recession characteristics. DRAINMOD was used to simulate hydrologic response from drained (24 m tile spacing) and undrained agricultural systems. Hydrograph analysis was conducted using programs PART and RECESS. Field monitoring data were obtained from several monitoring sites in Iowa typical of heavily drained and less‐drained regions. Results indicate that flow from tile drainage primarily affects the baseflow portion of a hydrograph, increasing annual baseflow in streams with seasonal increases primarily occurring in the late spring and early summer months. Master recession curves from tile‐drained watersheds appear to be more linear than less‐tiled watersheds although comparative results of the recession index k were inconsistent. Considering the magnitude of non‐point source pollutant loads coming from tile‐drained landscapes, it is critical that more in‐depth research and analysis be done to assess the effects of tile drainage on watershed hydrology if water quality solutions are to be properly evaluated. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Hydrology and Nitrogen Components of a Simple Rye Growth Model

Cover cropping practices are being researched to reduce artificial subsurface drainage nitrate-nitrogen (nitrate-N) losses from agricultural lands in the upper Mississippi watershed. A soil-plant-a...

Potential for a Rye Cover Crop to Reduce Nitrate Loss in Southwestern Minnesota

Cover cropping practices are being researched to reduce artificial subsurface drainage NO3–N losses from agricultural lands in the Upper Mississippi watershed. This study was designed to investigate the influences of fall planting date and climate on cereal rye (Secale cereale L.) biomass and N uptake in the spring, and to assess subsurface drainage NO3–N loss reductions. A soil–plant–atmosphere simulation model, RyeGro, was developed and used to predict rye cover crop establishment and growth, soil water balance, N cycling, and drainage NO3–N losses from mid‐September through May in southwestern Minnesota. An imbedded stochastic weather generator provided model climate inputs. Inclusion of a rye cover crop sown on 15 September reduced N losses by 11.1 kg N ha−1 or 45% for a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] crop rotation. Fall sowing dates of 1, 15, and 30 October resulted in reductions of 7.8, 5.8, and 4.6 kg N ha−1, respectively, by the end of May. Desiccation of the rye on 1 May resulted in reductions of 4.5, 2.2, 1.2, and 0.7 kg N ha−1, for the 15 September and 1, 15, and 30 October sowing dates, respectively. Cover cropping practice provides promising opportunities for reductions in N losses for cropping rotations wherein the primary crops are harvested before mid‐September and planted after mid‐May. We predict that a winter rye crop can reduce drainage NO3–N losses on average 7.4 kg N ha−1 for southwestern Minnesota if planted on 15 September and desiccated on 15 May.

Drip Irrigation of Tomato and Cotton Under Shallow Saline Ground Water Conditions

Artificial subsurface drainage is not an option for addressing the saline, shallow ground water conditions along the west side of the San Joaquin Valley because of the lack of drainage water disposal facilities. Thus, the salinity/drainage problem of the valley must be addressed through improved irrigation practices. One option is to use drip irrigation in the salt affected soil.

Selecting a calculation method to estimate sediment and nutrient loads in streams: Application to the Beaurivage River (Québec, Canada)

Estimation of sediment and nutrient loads is of crucial interest for a good assessment of water pollution. This paper proposes an overview of existing estimation methods and a framework to select the most suited one given available streamflow and concentration data. Correlations between contaminant concentration and streamflow should first be checked to generate missing concentration values by regression. However, correlations are not always strong, in which case the ratio estimator method is more appropriate. Given a 6-year data set (1989–1995) from the Beaurivage River (Québec, Canada) with, at best, a weekly sampling, the ratio estimator method was selected to estimate annual and seasonal loads of sediments and nutrients (N and P). Results show relatively steady annual loads (on average 8.1 and 1.1 kg ha yr −1 for total dissolved N and total P, respectively) and a low erosion rate (0.23 t ha yr −1). The results also confirm that nutrient and sediment transport via runoff is essentially a springtime process in this region, and they indicate that dissolved P represents the bulk of the total P load, most likely due to artificial subsurface drainage systems in the watershed. These results are compared to the results obtained by using averaging methods and to several other sources of information from literature, confirming the order of magnitude but highlighting some remaining uncertainties. Finally, some research avenues are proposed to improve the proposed framework and to investigate other estimation methods adapted to data characteristics.

Plant Growth Component of a Simple Rye Growth Model

Cover cropping practices are being researched to reduce artificial subsurface drainage nitrate-nitrogen (nitrate-N) losses from agricultural lands in the upper Mississippi watershed. A soil-plant-atmosphere simulation model, RyeGro, was developed to quantify the probabilities that a winter rye cover crop will reduce artificial subsurface drainage nitrate-N losses given climatic variability in the region. This article describes the plant growth submodel of RyeGro, Grosub, which estimates biomass production with a radiation use efficiency-based approach for converting intercepted photosynthetically active radiation to biomass. Estimates of nitrogen (N) uptake are based on an empirical plant N concentration curve. The model was calibrated with data from a three-year field study conducted on a Normania clay loam (fine-loamy, mixed, mesic Aquic Haplustoll) soil at Lamberton, Minnesota. The model was validated with data measured from a field trial in St. Paul, Minnesota. The cumulative rye aboveground biomass predictions for the calibration years differed by -0.45, 0.09, and 0.16 Mg ha-1 (-17%, 9%, and 32%), and the plant N uptake predictions differed by -10.5, 8.0, and 4.0 kg N ha-1 (-16%, 30%, and 21%) from the observed values. The predictions of biomass production and N uptake for the validation year varied by -1.4 Mg ha-1 and 16 kg N ha-1 (-27% and 24%) from the values observed in the field study, respectively. A local sensitivity analysis of eight input parameters indicated that model output is most sensitive to the maximum leaf area index and radiation use efficiency parameters. Grosub demonstrated the capability to predict seasonal aboveground biomass production of fall-planted rye in southwestern Minnesota within an accuracy of ±30% in years when production exceeds 1 Mg ha-1 by mid-May, and to predict seasonal rye N uptake within ±25% of observed values.