Surface Inlets Research Articles

Assessing the Effectiveness of Alternative Tile Intakes on Agricultural Hillslopes

Existing surface inlets behind terraces and water and sediment control basins (WASCoBs) were replaced with alternative tile intakes (ATIs) in agricultural fields of southeast Iowa. These ATIs consisted of a buried column of gravel atop woodchips. Computational, experimental, and field methods were used to design and evaluate the ATIs’ capacity to reduce sediment and nutrient export. Single-storm simulations using the Watershed Erosion Prediction Project (WEPP) provided boundary conditions for permeameter experiments that yielded a hydraulic conductivity for the layered gravel–woodchip configuration of 4.59 cm/s ± 0.36 cm/s. Additionally, a proportional amount of sediment was retained in the permeameter (42%) compared to the amount that settled on the permeameter surface (58%). Event monitoring of field-installed ATIs during three growing seasons measured a sediment trapping efficiency of 86 ± 12% that led to deposition rates of 5.44 ± 3.77 cm/yr, quantified with 210Pb profiles. Percent reduction values were 43% for nitrate and 17% for ortho-phosphate. Finally, long-term continuous-storm modeling using the WEPP suggested that these ATIs could withstand at least 75 25-year events before clogging. Modeling using the Agricultural Conservation Planning Framework suggested watershed-scale load reductions of 1.6% for NO3 and 1.4% for total P for ATIs draining 6.8% of the modeled watershed. Using ATIs in conjunction with WASCOBs and terraces, or as standalone practices, can be a cost-effective means for keeping sediment and nutrients in the landscape.

Using nutrient transport data to characterize and identify the presence of surface inlets in regions with subsurface drainage.

Surface inlets route ponded surface water into subsurface drainage networks and are prevalent throughout North America. Despite serving as a nutrient loss pathway, contributing to downstream water quality degradation, surface inlets are thought to be underreported in drainage studies within the literature. Previous studies have demonstrated the footprint that surface inlets have on nutrient transport and drainage effluent but are site specific and focused on individual events. Moreover, although their ubiquitous presence is assumed, no regional surface inlet database exists. To this end, a structured review was undertaken with two goals. First, the MANAGE Drain Load database, consisting of nearly 1,500 site-years of drainage and nutrient data, was analyzed to determine distinctions between areas with and without surface inlets. The median annual total phosphorus (TP) load was greater at site-years with surface inlets (0.40kg ha-1 ) than site-years without (0.21kg ha-1 ). The opposite emerged for dissolved nitrogen (DN) loads as site-years with surface inlet had a smaller median annual load (3.3kg ha-1 ) than site-years without (23.0kg ha-1 ). This relationship is attributed to immobile TP being transported primarily through overland flow and routed to subsurface drains via surface inlets and to relatively more mobile DN being subsurface driven, bypassed in settings with surface inlets. No statistical differences were found in annual drainage or ratios of particulate P to TP between site-years with and without surface inlets. Second, a logistic regression model was developed that predicts the presence of surface inlets within MANAGE. Eighteen percent of site-years and 21% of sites were predicted to have surface inlets.

Hydrologic assessment of blind inlet performance in a drained closed depression

Surface inlets installed in agricultural closed depressions can transport sediment- and nutrient-laden runoff directly to receiving streams or water bodies. Replacing tile risers with blind inlets has the potential to decrease these sediment and nutrient loads, but adoption of blind inlets has been met with hesitation from producers who fear that changes to the surface inlet may result in additional water ponding, crop damage, or crop loss. The objectives of this study were to assess hydrologic performance of blind inlets over time, and to determine whether blind inlets influenced the hydrology of a closed depression compared to a tile riser. Hydrograph characteristics including flow duration, time to peak flow, peak flow rate, and cumulative flow were evaluated for 549 storm events over a 12-year period (2006 to 2017) for a pair of closed depressions in northeastern Indiana. Surface water could be drained in both depressional areas with either a tile riser or blind inlet. Results showed that blind inlet infiltration rates declined approximately linearly over time (1.4 cm h⁻¹ y⁻¹). While changes in infiltration were largely controlled by annual tillage practices at the study sites, findings suggest that blind inlets have an effective service life of 8 to 10 years under the study conditions. Surface water management practices significantly influenced depression hydrology; however, the practices functioned differently between fields. Blind inlets did not influence the frequency of discharge, but they may increase or decrease the duration of flow and cumulative flow compared to a tile riser depending on the extent of subsurface tile drainage within the closed depression. Findings from this study underscore the inherent connections between surface and subsurface hydrologic processes in drained closed depressions and how these connections may influence both water quantity and water quality.

CoBAGNPS: A toolbox for simulating water and sediment control basin, WASCoB through AGNPS model

A WASCoB constituting a modest detention pond (berm), surface inlets and tile drains; designed to capture the flow and release it gradually into the drainage system is an efficient watershed BMP. Henceforth; a toolbox, CoBAGNPS for the AGNPS model, is developed to simulate WASCoBs through the AGNPS model. The toolbox utilizes the inputs from AGNPS, through the launching of an application for execution of the WASCoB module. Finally, the output files are generated after routing flow through WASCoBs. The toolbox was applied with a case study in the Gully creek watershed and one of its sub-basins (DFTILE sub-basin) located in Ontario, Canada. The toolbox reproduced the required outputs successfully. Henceforth, significantly enhancing the capability of the AGNPS model to simulate flow through a WASCoB and a network of WASCoBs. Furthermore; the efficiency of the drainage system is also analyzed under different scenarios of pipe risers and tile drains. Also, few scenario analyses were considered in which different diameter drainage pipes were considered to route flow for extreme events for WASCoB3 in the DFTILE sub-basin. A 375-mm diameter drainage pipe is efficient in routing flow for a 10-year 24-h design storm without it overtopping the berm. Finally, another component of the toolbox was tested, where the flow from the DFTILE sub-basin was directly routed to the outlet of the Gully creek watershed (GULGUL 5) through a drainage pipe of 200 mm with 1% slope, assuming a lag time. The hydrograph at the watershed outlet increased marginally due to the small size of the DFTILE sub-basin.

Inundation Patterns of Farmed Pothole Depressions with Varying Subsurface Drainage

HighlightsFarmed pothole depressions in the Des Moines Lobe were observed to fill due to runoff and shallow subsurface flow.Six of the eight observed potholes flooded for five or more days some time during the two years of observation.Subsurface drainage and surface inlets reduced but did not prevent yield-limiting flooding in the observed potholes. Abstract. The prairie pothole region (PPR) ranges from central Iowa to the northwest into Montana and south central Canada, totaling around 700,000 km2. This area contains millions of potholes, or enclosed topographical depressions, which often inundate with rainfall. Many are located in areas that have been converted to arable agricultural land through installation of artificial drainage. However, even with drainage, potholes will pond or have saturated soil conditions during and after significant rain events. The portion of the PPR that extends into Iowa is known as the Des Moines Lobe. In this two-year study, surface water depth data were collected hourly from eight prairie potholes in the Des Moines Lobe in central Iowa to determine the surface water hydrology. These potholes included surface and subsurface drained row crops and undrained retired land, allowing for drainage comparisons. Inundation lasted five or more days at least once at six of the eight potholes, including four potholes with surface inlets and subsurface drainage, which resulted in four of fourteen growing seasons not producing a yield in part of the pothole. Water balances of four different drainage intensities showed increased infiltration due to subsurface drainage and up to 78% of outflow due to surface inlet drainage. Overall, drainage decreased the number of average inundation days, but heavy precipitation events still caused lengthy inundation periods that resulted in crop loss. Keywords: Farmed wetlands, Prairie pothole, Tile drainage, Water balance.

Effects of land management on inundation of prairie pothole wetlands in the Des Moines Lobe using AnnAGNPS

The Prairie Pothole Region (PPR) of North America contains millions of shallow wetlands, called potholes, in a landscape that was originally midgrass and tallgrass prairie. Since the 1900s, the prairie pothole landscape has been altered through the installation of subsurface drainage to make the land suitable for agricultural production. Currently, many of these potholes are farmed but they are often areas of poor crop yields because of early growing season flooding. The objective of this study was to investigate the influence of different land use practices on depth, duration, and aerial extent of ponding in two potholes (termed Walnut and Bunny) in central Iowa. Three management scenarios were simulated and inundation levels were compared using the Annualized Agriculture Non-Point Source model (AnnAGNPS) — current: conventionally tilled farmed conditions in corn/soybean rotation with surface inlets in the potholes connecting to a subsurface drainage system; retired: pothole is converted to a mixture of grass, weeds, and low-growing brush, with surface inlets removed and the drainage system underneath the potholes disconnected; and conserved: conservation tillage throughout the field with surface inlets and drainage maintained in potholes. The average annual water depth for the conserved and retired scenarios was 7–8% lower than the average annual water depth for the current scenario. However, for the retired scenario, an increase in inundation was observed in Bunny because disconnecting the surface inlets reduced infiltration in the model. The potholes tend to flood more frequently in the early stages of plant development, which can lead to delayed management operations and potentially reduced yields. Over the 17 year simulation period, Bunny pothole exceeded its maximum volume storage capacity and overflowed five times. This information is important to prioritize areas for and to understand the hydrologic impacts of pothole restoration efforts in intensive agricultural landscapes.

CoBAGNPS: A Toolbox to Estimate Sediment Removal Efficiency of WASCoBs–Pipe Risers and Blind Inlets

Water and Sediment Control Basin (WASCoB) is an important BMP constructed along concentrated flow-paths (gullies etc.) to control the movement of water and sediment within a watershed. A WASCoB constitutes of a berm, surface inlets, and a drainage pipe to route water into a ditch. Direct runoff ponded behind the berm is routed through surface inlets into an underground drainage pipe. Therefore, surface inlets are an exceedingly important constituent of a WASCoB. Further pipe risers and blind inlets are the two most common type of surface inlets used. Therefore, maximum sediment removal efficiency of WASCoBs at a watershed-scale can be attained by the appropriate selection of a surface inlet, since the efficiency of a WASCoB is greatly impacted by the quantity of runoff and sediment leaving the surface inlet. In this study a toolbox was developed viz., CoBAGNPS to compute the sediment removal efficiency of pipe risers and blind inlets. A watershed-scale model (AGNPS) was integrated within the toolbox. Output files of the AGNPS model are fed as input files into the toolbox where a sediment routing module is programmed separately for pipe risers and blind inlets to obtain the sediment removal efficiency for each type of surface inlet. Further, the sediment routing module programmed for blind inlets integrates the AGNPS model with the HYDRUS 1-D model. The toolbox developed was applied to the Gully Creek watershed in Ontario, and the sediment load routed through pipe risers and blind inlets were compared.

Quantifying hydrologic connectivity of wetlands to surface water systems

Abstract. Hydrologic connectivity among wetlands is poorly characterized and understood. Our inability to quantify this connectivity compromises our understanding of the potential impacts of wetland loss on watershed structure, function and water supplies. We develop a computationally efficient, physically based subsurface–surface hydrologic model to characterize both the subsurface and surface hydrologic connectivity of geographically isolated wetlands and explore the time and length variations in these connections to a river within the Prairie Pothole Region of North America. Despite a high density of geographically isolated wetlands (i.e., wetlands without surface inlets or outlets), modeled connections show that these wetlands are not hydrologically isolated. Subsurface connectivity differs significantly from surface connectivity in terms of timing and length of connections. Slow subsurface connections between wetlands and the downstream river originate from wetlands throughout the watershed, whereas fast surface connections were limited to large events and originate from wetlands located near the river. This modeling approach provides first ever insight on the nature of geographically isolated wetland subsurface and surface hydrologic connections to rivers, and provides valuable information to support watershed-scale decision making for water resource management.

Assessment of Surface Inlets Performance on Sediment Transport to Subsurface Drainage System

Abstract. Infield ponding can have detrimental effects on crops and soils and result in reduced yields and increased sedimentation. Surface inlets are commonly used to prevent or reduce incidents of ponding. In this study, the flow and sediment transport characteristics of four surface inlets–the standard Hickenbottom inlet, two inlets (standard and QuickDrain®) designed by Ag-Solutions, and an inlet developed by AgriDrain–were evaluated in both laboratory and field settings with simulation rainfall. The Hickenbottom and QuickDrain® Ag-solutions inlet had higher sediment concentration and sediment load compared to the other inlets. The average sediment concentration and sediment load for Hickenbottom and QuickDrain® Ag-solutions inlets were measured to be 3532.70 mg/L, 64919.05 mg/min, and 3104.31 mg/L, 24880.69 mg/min, respectively. The measured sediment concentration and sediment load for standard Ag-solutions inlet were smaller than Hickenbottom and QuickDrain® Ag-solutions inlets but higher than the AgriDrain inlet. The AgriDrain inlet was the most effective among the four inlets in reducing sediment (66% concentration and 23.2% load compared to Hickenbottom) (p

Capturing Excess Nutrients from Waterways

Capturing Excess Nutrients from Waterways

Nutrient management planners' feedback on New York and Pennsylvania phosphorus indices

State phosphorus indices (PIs) are being evaluated across the United States due to variability in phosphorus (P) management recommendations and questions about the lack of water quality improvement in some watersheds. Nutrient management planners in New York (NY) and Pennsylvania (PA) were surveyed via two separate “but related” questionnaires to document perspectives on the current NY-PI and PA-PI and to obtain recommendations for improvements. Many planners were content with the current versions of the PIs but felt improvements could be made to more strongly discourage application of manure under conditions of high P loss potential and better promote certain best management practices. The NY planners felt that the NY-PI should discourage manure application during winter and to fields near streams, and should more strongly promote manure incorporation or injection, establishment of cover crops, ground coverage with crop residues, and implementation of setbacks and vegetated buffers. Similarly, the PA planners felt that the PA-PI should more strongly discourage manure application to fields with insufficient ground cover, near subsurface drainage and surface inlets, and during winter. In addition, the PA planners said the PA-PI should more strongly encourage soil conservation practices such as no-till, use of cover crops, and vegetated buffers. Results of the survey suggest common experiences and viewpoints among planners in NY and PA, resulting in a valuable on-the-ground assessment of the PIs as a nutrient management planning tool in both states, and the potential for development of a single, physiographic region PI.

Atrazine Sorption by Biochar, Tire Chips, and Steel Slag as Media for Blind Inlets: A Kinetic and Isotherm Sorption Approach

Surface inlets are installed in subsurface drainage systems to reduce ponding duration and surface runoff, but can contribute to water quality concerns by allowing water to directly enter buried drains. Blind inlets consist of perforated pipes covered with gravel and are separated from an overlying sand layer by a geotextile membrane and have been shown to be more effective in reducing losses of sediment, nutrients, and pesticides than typical tile line risers. In this study, we investigated whether the effectiveness of blind inlets to sorb pollutants, with emphasis on the herbicide atrazine, could be further improved by amended them with materials other than limestone. The media, shredded tires (tire chips), electric arc steel furnace slag (steel slag), and oak-derived biochar were chosen because they are readily available, inexpensive, and do not present environmental concerns. Kinetic sorption and isotherms were determined to ascertain atrazine sorption by these materials, in addition to testing for potential metal leaching using the Synthetic Precipitation Leaching Procedure (SPLP) and the Toxicity Characteristic Leaching Procedure (TCLP). The kinetic data were fitted using pseudo first- and second-order reaction equations and indicated that atrazine sorption rate was 38 times faster and equilibrium was reached 5 times earlier for biochar than tire chips. The 24-h sorption isotherm data were fitted to the Freundlich sorption equation. The sorption coefficient for biochar was higher than for tire chips, steel slag, and limestone. Per the SPLC and TLCP tests, there was no leaching of heavy metals at levels of environmental concern. Our results suggested that the effectiveness of blind inlets as well as other conservation practices that include filter media such as rain gardens and filter socks could be improved by incorporating more reactive materials than sand and gravel with biochar being a particularly effective alternative.

Effect of replacing surface inlets with blind or gravel inlets on sediment and phosphorus subsurface drainage losses.

Open surface inlets that connect to subsurface tile drainage systems provide a direct pathway for movement of sediment, nutrients, and agrochemicals to surface waters. This study was conducted to determine the reduction in drainage effluent total suspended sediment (TSS) and phosphorus (P) concentrations and loads when open surface inlets were replaced with blind (in gravel capped with 30 cm of soil) or gravel (in very coarse sand/fine gravel) inlets. In Indiana, a pair of closed depressions in adjacent fields was fitted with open inlet tile risers and blind inlets in 2005 and monitored for flow and water chemistry. Paired comparisons on a storm event basis during the growing season for years 2006 to 2013 showed that TSS loads were 40.4 and 14.4 kg ha event for tile risers and blind inlets, respectively. Total P (TP) and soluble reactive P (SRP) loads were 66 and 50% less for the blind inlets, respectively. In Minnesota, TSS and SRP concentrations were monitored for 3 yr before and after modification of 24 open inlets to gravel inlets in an unreplicated large-field on-farm study. Median TSS concentrations were 97 and 8.3 mg L and median SRP concentrations were 0.099 and 0.064 mg L for the open inlet and gravel inlet periods, respectively. Median TSS and SRP concentrations were elevated for snowmelt vs. non-snowmelt seasons for open and gravel inlets. Both replacement designs reduced suspended sediment and P concentrations and loads. The Indiana study suggests blind inlets will be effective beyond a 10-yr service life.

Phosphorus transport in agricultural subsurface drainage: a review.

Phosphorus (P) loss from agricultural fields and watersheds has been an important water quality issue for decades because of the critical role P plays in eutrophication. Historically, most research has focused on P losses by surface runoff and erosion because subsurface P losses were often deemed to be negligible. Perceptions of subsurface P transport, however, have evolved, and considerable work has been conducted to better understand the magnitude and importance of subsurface P transport and to identify practices and treatments that decrease subsurface P loads to surface waters. The objectives of this paper were (i) to critically review research on P transport in subsurface drainage, (ii) to determine factors that control P losses, and (iii) to identify gaps in the current scientific understanding of the role of subsurface drainage in P transport. Factors that affect subsurface P transport are discussed within the framework of intensively drained agricultural settings. These factors include soil characteristics (e.g., preferential flow, P sorption capacity, and redox conditions), drainage design (e.g., tile spacing, tile depth, and the installation of surface inlets), prevailing conditions and management (e.g., soil-test P levels, tillage, cropping system, and the source, rate, placement, and timing of P application), and hydrologic and climatic variables (e.g., baseflow, event flow, and seasonal differences). Structural, treatment, and management approaches to mitigate subsurface P transport-such as practices that disconnect flow pathways between surface soils and tile drains, drainage water management, in-stream or end-of-tile treatments, and ditch design and management-are also discussed. The review concludes by identifying gaps in the current understanding of P transport in subsurface drains and suggesting areas where future research is needed.

Hydrogeochemical features of Lake Ngozi (SW Tanzania)

Located on the triple rift junction hosting the Karonga-Usungu depression in Tanzania, Lake Ngozi is the second largest crater lake of the East African Rift. The lake has a number of peculiar features: it has a near constant water level, no permanent surface inlets and outlets, it is vertically well-mixed, with homogeneous distribution of temperature and chemical composition, and it is characterised by near neutral to slightly acid Na–Cl waters of comparatively high salinity and high P–CO2. Based on the different chemical signature of surface and ground waters (low-Cl type) from lake waters, mass balance methods have been applied to investigate lake dynamics. Water enters the lake mainly by precipitation and groundwater inflow, and leaves by groundwater outflow and evaporation. A large groundwater outflow of 2.4myr−1 has been estimated. The high salinity, Na–Cl signature of Lake Ngozi waters, together with 3He/4He ratios measured on dissolved gases (between 7 and 8.3 Ra) and high-PCO2 values estimated all along the water vertical column indicate the inflow of deep-seated fluids, likely magmatic in origin, into the lake. The existence of a hydrothermal system possibly at 250°C in the root of the volcanic edifice is also hypothesised on the basis of solute geothermometry. Despite the current lack of vertical stratification, the lake is suspected to act as condenser for CO2 and other gases of deep magmatic origin, and should be then further monitored for the risk of limnic eruptions as well as for environmental and climatic concerns.

Nitrogen loading to offsite waters from liquid swine manure application under different drainage and tillage practices

Abstract Too much nitrogen (N) in surface water is harmful to aquatic life. Subsurface drains, some along with surface inlets, are commonly used for drainage of agricultural land in humid regions and contribute unknown N amounts to surface water. Quantification of relative amounts moving through different pathways and characterization of the sources are needed to mitigate movement. The major pathways to surface water, namely, runoff and tile drains, were monitored over 2 yr, from fields having sub-catchments with no-(Ni), hickenbottom-(Hb) or blind-(Bi) surface inlets, or natural drainage (ND) to determine the effect of drainage system configuration and associated management practices on N loading. The fields were managed under either common practice (CP) of conventional tillage with broadcast incorporated liquid swine manure (LSM) or minimum tillage (MT) with injected LSM. Tile drainage increased NO3-N load to surface water by 36 ± 17 kg ha−1 [sum of overland + subsurface over two non-growing seasons (NGSs) and one growing season] as compared with ND. Surface inlet or its type had little effect on N movement through the drainage systems. Application-induced preferential flow of LSM to drainage tile occurred with injection at one of two fields in the drain installation year, but not in the following year, contributing 80% of the annual NH4-N load from drainage tile, but only 5% of the total N (Nt) overland + subsurface movement, which consisted of 82% NO3-N (average of three tile drained catchments). Loading of N to surface water both overland and through tile drains was dominated by a few events, particularly snowmelt. Runoff waters had elevated NO3-N concentrations on some NGS events, particularly from CP management. Surface runoff accounted for up to 27% of the total (overland + subsurface) NO3-N load to surface water in the NGS under CP management, though amounts varied from different catchments. Results indicated that year-round monitoring is important when measuring systems impacts on N loading; and that to achieve watershed scale impact, along with controlling N movement to drainage tile, strategies effective on frozen ground and during snowmelts, when much of the movement occurs, are needed.

Sediment and Nutrient Contributions from Subsurface Drains and Point Sources to an Agricultural Watershed

Excess sediment and nutrients in surface waters can threaten aquatic life. To determine the relative importance of subsurface drainage as a pathway for movement of sediment and nutrients to surface waters, loading from various tile systems was compared to that from sewage treatment plants (STP) within the same watershed. Movement through tiles comprised 1 to 8% of estimated total (overland plus tile) annual sediment loading from the respective areas drained by the tile. Load during the growing season from five closed drainage systems without surface inlets averaged 5 kg sediment/ha, 0.005 kg dissolved reactive P (DRP)/ha, 0.003 kg NH4-N/ha, and 3.8 kg NO3-N/ha; and from two open drainage systems with surface inlets averaged 14 kg sediment/ha, 0.03 kg DRP/ha, 0.04 kg NH4-N/ha, and 3.1 kg NO3-N/ha. The eight STP contributed about 44 530 kg suspended sediments, 3380 kg total P, 1340 kg NH4-N, and 116 900 kg NO3-N to the watershed annually. Drainage systems added less NH4-N and P, but more NO3-N and suspended solids to surface waters than STP. Tile drainage pathways for NO3-N, STP in the case of P, and overland pathways for sediment are indicated as targets to control loading in artificially drained agricultural watersheds.

Element fluxes in watershed-lake ecosystems recovering from acidification: Plešné Lake, the Bohemian Forest, 2001–2005

Fluxes of major ions and nutrients were measured in the watershed-lake ecosystem of a strongly acidified lake, Plesne jezero (Plesne Lake), in the Czech Republic in hydrological years from 2001 through 2005. The lake is situated in a Norway spruce forest and has a steep watershed between elevations of 1090 and 1378 m. The average water input and output from the ecosystem was 1372 mm and 1157 mm (37 L km−2 s−1), respectively, and the water residence time averaged 306 days. Despite ecosystem recovery from acidification occurring since the late 1980s, the Plesne watershed was an average net source of 25 mmol SO42− m−2 yr−1. Nitrogen saturation of the watershed caused low retention of the deposited inorganic N (< 44% on average) before 2004. Then, the watershed became a net source of 28–32 mmol m−2 yr−1 of inorganic N in the form of NO3− due to climatic effects (a dry summer in 2003 and a cold winter in 2004) and forest dieback caused by a bark beetle attack in 2004. Nitrogen transformations and SO42− release were the dominant terrestrial sources of H+ (72 and 49 mmol m−2 yr−1, respectively) and the watershed was a net source of 24 mmol H+ m−2 yr−1. Ionic composition of surface inlets showed seasonal variations, with the most pronounced changes in NO3−, ionic Al (Ali), and DOC concentrations, while the composition of subsurface inlets was more stable. The in-lake biogeochemical processes reduced on average 59% of the incoming H+ (251 mmol H+ m−2 yr−1 on a lake-area basis). NO3− assimilation and denitrification, photochemical and microbial decomposition of allochthonous organic acids, and SO42− reduction in the sediments were the most important aquatic H+ consuming processes (358, 121, and 59 mmol H+ m−2 yr−1, respectively), while hydrolysis of Ali was the dominant in-lake H+ generating process (233 mmol H+ m−2 yr−1). Photochemical liberation from organic complexes was an additional in-lake source of Ali. The net in-lake retention or removal of total phosphorus, total nitrogen, and silica were on average 50%, 27%, and 23%, respectively. The lake was a net source of NH4+ due to a cease in nitrification (pH < 5) and from NH4+ production by dissimilation exceeding its removal by assimilation.

Tillage and Nutrient Source Effects on Water Quality and Corn Grain Yield from a Flat Landscape

Beneficial effects of leaving residue at the soil surface are well documented for steep lands, but not for flat lands that are drained with surface inlets and tile lines. This study quantified the effects of tillage and nutrient source on tile line and surface inlet water quality under continuous corn (Zea mays L.) from relatively flat lands (<3%). Tillage treatments were either fall chisel or moldboard plow. Nutrient sources were either fall injected liquid hog manure or spring incorporated urea. The experiment was on a Webster-Canisteo clay loam (Typic Endoaquolls) at Lamberton, MN. Surface inlet runoff was analyzed for flow, total solids, NO(3)-N, NH(4)-N, dissolved P, and total P. Tile line effluent was analyzed for flow, NO(3)-N, and NH(4)-N. In four years of rainstorm and snowmelt events there were few significant differences (p < 0.10) in water quality of surface inlet or tile drainage between treatments. Residue cover minimally reduced soil erosion during both snowmelt and rainfall runoff events. There was a slight reduction in mineral N losses via surface inlets from manure treatments. There was also a slight decrease (p = 0.025) in corn grain yield from chisel-plow plots (9.7 Mg ha(-1)) compared with moldboard-plow plots (10.1 Mg ha(-1)). Chisel plowing (approximately 30% residue cover) alone is not sufficient to reduce nonpoint source sediment pollution from these poorly drained flat lands to the extent (40% reduction) desired by regulatory agencies.

The environmental status of a Kashmir Himalayan wetland game reserve: Aquatic plant communities and eco‐restoration measures

AbstractThe data (November 2000 – October 2001) are presented on environmental status, hydrology, sedimentation rate, water quality and macrophytic community architecture of an important game reserve (Hokersar Wetland) in the Kashmir Himalayan valley. Of the total water input, 91% was contributed from surface inlets and just 9% through precipitation. Of the total surface water output, 67% occurred through outlets while evapotranspiration and other losses accounted for 33%. The net annual sediment accumulation was principally a function of suspended load carried by Doodganga inlet. The ecosystem supports diverse aquatic plant communities (emergents, rooted–floating leaf type, free‐floating leaf type, submersed type) marked by striking variability in composition, frequency and extent of colonization. Several ecological factors, such as habitat loss related to siltation, pollution, expanding agricultural activities and drastic hydrological fluctuations, have induced considerable changes in the dynamics and distribution pattern of sustained biota. The shift in macrophytic community structure is evidenced by the decline of Nelumbio nucifera and the near‐disappearance of some economically important plants (Euryale ferox, Acorus calamus). The shrinkage of the wetland area, once spread over 1800 ha, by ≈28% is a cause for environmental concern. The paper highlights the rapidly deteriorating environmental status of the Kashmir Himalayan Hokersar Wetland game reserve and stresses the need for its urgent ecological restoration.