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Leaching of Nitrogen, Phosphorus and Other Solutes from a Controlled Drainage Cultivated Peatland in Ruukki, Finland
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Nitrogen (N) and phosphorus (P) losses, via both surface runoff and subsurface drainage water, were monitored in an agricultural field in northern Sweden for 32 yr. The objective was to determine losses of N and P in a long‐term perspective in relation to meteorological factors and impacts of agricultural land use, with a focus on relative contributions of surface runoff and subsurface drainage water to N and P losses. In order to collect surface runoff water, an embankment was installed on three sides of the field, and the fourth side had an open ditch that drove runoff water to a measuring station. Subsurface water draining from the field was collected in a fishbone‐shaped drainage system that terminated at the measuring station. In 50% of years (16/32), mean annual concentration of total N (TN) was significantly higher in subsurface drainage water than in surface runoff water. An opposing trend was seen for total P (TP), with mean annual concentration being significantly higher in surface runoff water than in subsurface drainage water in all but 3 of the 32 yr monitored. Years with a barley crop had higher TN concentration in subsurface drainage water but no difference in surface runoff compared with years with ley. In contrast, years with barley had lower TN concentration in surface runoff than years with ley, with no difference in TP in subsurface drainage water.
The off-site effects of agricultural organic soils include the leaching of N, P, and organic carbon (OC) to watercourses and CO2, CH4, and N2O emissions into the atmosphere. The aim of this study was to quantify how the thickness of organic layers affects these loads. A 19.56-ha experimental field drained by subsurface pipes was established in Ruukki, northwestern Finland. Three plots had a 60–80 cm-thick sedge peat layer and three others had a thickness of 20 cm or less. The drainage pipes lie in mineral soil that, in this field, contains sulfidic material. This study documents the experimental settings and reports on the leaching of substances in the first two years, as well as CO2, CH4 and N2O emissions during eight weeks in one summer. Total N (TN) and OC loads were higher from the thicker peat plots. The mean TN loads during a hydrological year were 15.4 and 9.2 kg ha⁻¹ from the thicker and thinner peat plots, respectively, with organic N representing 36% of TN load. Total P (TP) load averaged 0.27 kg ha⁻¹ yr⁻¹. Dissolved P load represented 63 and 36% of TP in the thicker peat area and only 23 and 13% in the thinner peat area, and was thus increased upon peat thickness. These N and P loads through the subsurface drainage system represented roughly 83% of TN and 64% of TP loads from this field. There were no clear differences in greenhouse gas emissions among the plots during the eight-week monitoring period. Slowly oxidizing sulfide in the subsoil resulted in annual leaching of 147 kg S ha⁻¹, almost ten times that of non-sulfidic soils. Our first results emphasize the effect of the peat thickness on the leaching of substances and warn about considering all organic soils as a single group in environmental assessments.
Most studies on the effects of tillage operations documented the effects of tillage on losses through surface runoff. On flat areas, the subsurface runoff is the dominating pathway for water, soil and nutrients. This study presents results from a five-year plot study on a flat area measuring surface and subsurface runoff losses. The treatments compared were A) autumn ploughing with oats, B) autumn ploughing with winter wheat and C) spring ploughing with spring barley (n = 3). The results showed that subsurface runoff was the main source for soil (67%), total phosphorus (76%), dissolved reactive phosphorus (75%) and total nitrogen (89%) losses. Through the subsurface pathway, the lowest soil losses occurred from the spring ploughed plots. Losses of total phosphorus through subsurface runoff were also lower from spring ploughing compared to autumn ploughing. Total nitrogen losses were higher from autumn ploughing compared to other treatments. Losses of total nitrogen were more influenced by autumn ploughing than by a nitrogen surplus in production. Single extreme weather events, like the summer drought in 2018 and high precipitation in October 2014 were crucial to the annual soil and nutrient losses. Considering extreme weather events in agricultural management is a necessary prerequisite for successful mitigation of soil and nutrient losses in the future.
Besides causing acidification, acid sulfate (AS) soils contain large nitrogen (N) stocks and are a potential source of N loading to waters and nitrous oxide (N2O) emissions. We quantified the stocks and flows of N, including crop yields, N leaching, and N2O emissions, in a cultivated AS soil in western Finland. We also investigated whether controlled drainage (CD) and sub-irrigation (CDI) to keep the sulfidic horizons inundated can alleviate N losses. Total N stock at 0–100 cm (19.5 Mg ha⁻¹) was smaller than at 100–200 cm (26.6 Mg ha⁻¹), and the mineral N stock was largest below 170 cm. Annual N leaching (31–91 kg N ha⁻¹) plus N in harvested grain (74–122 kg N ha⁻¹) was 148% (range 118–189%) of N applied in fertilizers (90–125 kg N ha⁻¹) in 2011–2017, suggesting substantial N supply from soil reserves. Annual emissions of N2O measured during 2 years were 8–28 kg N ha⁻¹. The most probable reasons for high N2O emission rates in AS soils are concomitant large mineral N pools with fluctuating redox conditions and low pH in the oxidized subsoil, all favoring formation of N2O in nitrification and denitrification. Although the groundwater level was higher in CD and CDI than in conventional drainage, N load and crop offtake did not differ between the drainage methods, but there were differences in emissions. Nitrogen flows to the atmosphere and drainage water were clearly larger than those in non-AS mineral soils indicating that AS soils are potential hotspots of environmental impacts.
Nonpoint source phosphorus (P) and nitrogen (N) pollution from agriculture is a global concern. Planting a cover crop after harvesting annual crops such as maize may help mitigate nutrient transport risk to surface and groundwater. Few studies have focused on the impact of a winter rye cover crop on both surface runoff (SR) and tile drainage (TD) water quality. Here, we measured N and P losses in SR and TD from maize plots grown with and without a winter rye cover crop. Four plots (46 × 23 m) in northern New York, USA, equipped with automated SR and TD flow monitoring were planted with winter rye (Secale cereal) in 2016 and 2017 after maize silage harvest. Plots were managed as typical silage fields for dairy farms in the region and received fertilizer and manure applications. Dissolved reactive P (DRP), total P (TP), nitrate-N, total N (TN), and total suspended solids (TSS) loads were monitored from 4/7/16 to 6/29/17. Cumulative SR (volumetric depth equivalent) was 1.8-fold lower for rye compared to control plots. Although runoff and loading were variable, cumulative TSS, TP, and DRP losses were approximately 3-fold lower for rye plots compared to control. Cumulative TN and nitrate-N loads for TD were similar; however, cumulative TN loss for SR was lower for rye plots. Surface runoff was the main pathway of P loss (> 90% of DRP and TP loss) with > 90% of cumulative P exported from 2017 snowmelt events. Results suggest winter rye mitigated N and P transport risk in SR compared to the common practice of leaving maize silage fields bare after harvest.
Cover crops are well recognized as a tool to reduce NO 3 ⁻ leaching from agroecosystems. However, their effectiveness varies from site to site and year to year depending on soil, cash and cover crop management, and climate. We conducted a meta‐analysis using 238 observations from 28 studies (i) to assess the overall effect of cover crops on NO 3 ⁻ leaching and subsequent crop yields, and (ii) to examine how soil, cash and cover crop management, and climate impact the effect of non‐leguminous cover crops on NO 3 ⁻ leaching. There is a clear indication that nonleguminous cover crops can substantially reduce NO 3 ⁻ leaching into freshwater systems, on average by 56%. Nonlegume–legume cover crop mixtures reduced NO 3 ⁻ leaching as effectively as nonlegumes, but significantly more than legumes. The lack of variance information in most published literature prevents greater insight into the degree to which cover crops can improve water quality. Among the factors investigated, we identified cover crop planting dates, shoot biomass, and precipitation relative to long‐term mean precipitation as potential drivers for the observed variability in nonleguminous cover crop effectiveness in reducing NO 3 ⁻ leaching. We found evidence indicating greater reduction in NO 3 ⁻ leaching with nonleguminous cover crops on coarse‐textured soils and during years of low precipitation (<90% of the long‐term normal). Earlier fall planting and greater nonleguminous shoot biomass further reduced NO 3 ⁻ leaching. Overall, this meta‐analysis confirms many prior studies showing that nonleguminous cover crops are an effective way to reduce NO 3 ⁻ leaching and should be integrated into cropping systems to improve water quality.
Core Ideas
Nonleguminous cover crops reduced NO 3 ⁻ leaching by 56% over no cover crop controls.
Nonlegume–legume mixtures reduced NO 3 ⁻ leaching equivalent to nonlegumes, but significantly more than legumes.
Cover crop planting date, shoot biomass, and precipitation affected nonlegume effects on NO 3 ⁻ leaching.
Nonlegumes reduced NO 3 ⁻ leaching more effectively on coarse‐textured soils and in drier years.
Earlier planting dates and greater shoot biomass enhanced NO 3 ⁻ leaching reductions with nonlegumes.
No‐till as a water protection measure is highly efficient in controlling erosion and particulate P (PP) loss but tends to increase dissolved reactive P (DRP) concentrations in runoff water. In a 9‐yr field study on a clay soil in Southwest Finland, the effects of no‐till and autumn plowing on surface runoff and subsurface drainage water quality were compared. The site had a 2% slope and was under spring cereal cropping, with approximately replacement fertilizer P rates. Vertical stratification of soil‐test P that had developed during a preceding 6‐yr grass ley was undone by plowing but continued to develop under no‐till. During the 9‐yr study period, no‐till soil had 27% lower cumulative total P losses than plowed soil (10.0 vs. 13.7 kg total P ha ⁻¹ ). Concentrations and losses of PP were clearly lower under no‐till than under plowing (5.6 vs. 12.3 kg PP ha ⁻¹ ), but DRP loss showed the opposite trend (4.3 vs. 1.4 kg DRP ha ⁻¹ ). There was an increasing trend in subsurface drainflow DRP concentration under no‐till, possibly because of development of a conductive pore structure from soil surface to drain depth. The potential benefit of no‐till in water protection depends on how much of the PP transported to water is transformed into a bioavailable form and used by aquatic organisms. The beneficial effect of no‐till in controlling P‐induced eutrophication at the study site would only be realized if the bioavailable share of PP exceeds 43%. Otherwise, no‐till would not be an efficient eutrophication control measure at this site.
Core Ideas
No‐till decreased total P losses by 27% compared with autumn plowing.
No‐till produced 4.5‐fold higher DRP loss and 54% lower PP loss than plowing.
When changes in DRP and PP are opposite, TP changes should be interpreted with caution.
In this case, the effect on eutrophication largely depends on PP bioavailability.
At the study site, increased DRP load is compensated if PP bioavailability is >43%.
Thoroughly updated and now in full color, the 15th edition of this market leading text brings the exciting field of soils to life. Explore this new edition to find:
A comprehensive approach to soils with a focus on six major ecological roles of soil including growth of plants, climate change, recycling function, biodiversity, water, and soil properties and behavior.
New full-color illustrations and the use of color throughout the text highlights the new and refined figures and illustrations to help make the study of soils more efficient, engaging, and relevant.
Updated with the latest advances, concepts, and applications including hundreds of key references.
New coverage of cutting edge soil science. Examples include coverage of the pedosphere concept, new insights into humus and soil carbon accumulation, subaqueous soils, soil effects on human health, principles and practice of organic farming, urban and human engineered soils, new understandings of the nitrogen cycle, water-saving irrigation techniques, hydraulic redistribution, soil food-web ecology, disease suppressive soils, soil microbial genomics, soil interactions with global climate change, digital soil maps, and many others
Applications boxes and case study vignettes bring important soils topics to life. Examples include “Subaqueous Soils—Underwater Pedogenesis,” “Practical Applications of Unsaturated Water Flow in Contrasting Layers,” “Soil Microbiology in the Molecular Age,” and "Where have All the Humics Gone?”
Calculations and practical numerical problems boxes help students explore and understand detailed calculations and practical numerical problems. Examples include “Calculating Lime Needs Based on pH Buffering,” “Leaching Requirement for Saline Soils,” "Toward a Global Soil Information System,” “Calculation of Nitrogen Mineralization,” and “Calculation of Percent Pore Space in Soils.”
About 62 percent of Finland’s current surface area has been covered by the waters of the Baltic basin at some stage. The highest shorelines are located at a present altitude of about 220 metres above sea level in the north and 100 metres above sea level in the south-east. The nature of the Baltic Sea has alternated in the course of its four main postglacial stages between a freshwater lake and a brackish water basin connected to the outside ocean by narrow straits. This article provides a general overview of the principal stages in the history of the Baltic Sea and examines the regional influence of the associated
shore displacement phenomena within Finland. The maps depicting the various stages have been generated digitally by GIS techniques.
Following deglaciation, the freshwater Baltic Ice Lake (12,600–10,300 BP) built up against the ice margin to reach a level 25 metres above that of the ocean, with an outflow through the straits of Öresund. At this stage the only substantial land areas in Finland were in the east and south-east. Around 10,300 BP this ice lake discharged through a number of channels that opened up in central Sweden until it reached the ocean level, marking the beginning of the mildly saline Yoldia Sea stage (10,300–9500 BP). As the connecting channels rose above sea level, however, the Baltic Sea became confined once more, to form the Ancylus Lake (9500–8000 BP). During its existence the outflow channel to the ocean shifted to the Straits of Denmark and the major lake systems of central Finland became isolated from the Baltic basin. After the brief Mastogloia transition phase, a greater influx of saline water began to take place through the Straits of Denmark, marking the Litorina Sea stage (7500–
4000 BP), to be followed by a somewhat less saline stage known as the Limnea Sea. After a transgressive period early in the Litorina Sea stage, shoreline displacement in Finland has proceeded at a steadily declining rate.
Nitrate–nitrogen (NO3–N) as well as dissolved organic carbon (DOC) and nitrogen (DON) concentrations and losses were studied for three and two years, respectively, in a small catchment dominated by a degraded peatland used as intensive grassland. Concentrations in the shallow groundwater were spatially and temporally very variable, with NO3–N being the most dynamic component (7.3 ± 12.5 mg/L) and ranging from 0 to 79.4 mg/L. Average NO3–N concentrations of 10.3 ± 5.4 mg/L (0 to 25.5 mg/L) in the ditch draining the catchment and annual NO3–N losses of 19, 35 and 26 kg/ha confirmed drained peatlands as an important source of diffuse N pollution. The highest NO3–N losses occurred during the wettest year. Resulting from concentration of 2.4 ± 0.8 mg/L (0.7 to 6.2 mg/L), DON added a further 4.5 to 6.4 kg/ha to the N losses and thus formed a relevant (15%) component of the total N losses. Ditch DOC concentrations of 24.9 ± 5.9 mg/L (13.1 to 47.7 mg/L) resulted in DOC losses of 66 kg/ha in the wet year of 2006/2007 and 39 kg/ha in the dry year of 2007/2008. Ditch DOC concentration were lower than the groundwater DOC concentration of 50.6 ± 15.2 mg/L (14.9 to 88.5 mg/L). Both DOC and N concentrations were governed by hydrological conditions, but NO3–N reacted much faster and clearer on rising discharge rates than DOC, which tended to be higher under drier conditions. In the third year of the study, the superposition of a very wet summer and land use changes from grassland to arable land in a part of the catchment suggests that, under re-wetting conditions with a high groundwater table in summer, NO3–N would diminish quickly, while DOC would remain on a similar level. Further intensification of the land use, on the other hand, would increase N losses to receiving water bodies.
Anthropogenic drainage of peatlands releases additional greenhouse gases to the atmosphere, and dissolved carbon (C) and nutrients to downstream ecosystems. Rewetting drained peatlands offers a possibility to reduce nitrogen (N) and C losses. In this study, we investigate the impact of drainage and rewetting on the cycling of dissolved C and N as well as on dissolved gases, over a period of 1 year and a period of 4 months. We chose four sites within one Atlantic bog complex: a near-natural site, two drained grasslands with different mean groundwater levels and a former peat cutting area rewetted 10 years ago.
Our results clearly indicate that long-term drainage has increased the concentrations of dissolved organic carbon (DOC), ammonium, nitrate and dissolved organic nitrogen (DON) compared to the near-natural site. DON and ammonium contributed the most to the total dissolved nitrogen. Nitrate concentrations below the mean groundwater table were negligible. The concentrations of DOC and N species increased with drainage depth. In the deeply-drained grassland, with a mean annual water table of 45 cm below surface, DOC concentrations were twice as high as in the partially rewetted grassland with a mean annual water table of 28 cm below surface. The deeply drained grassland had some of the highest-ever observed DOC concentrations of 195.8 ± 77.3 mg L−1 with maximum values of >400 mg L−1. In general, dissolved organic matter (DOM) at the drained sites was enriched in aromatic moieties and showed a higher degradation status (lower DOC to DON ratio) compared to the near-natural site. At the drained sites, the C to N ratios of the uppermost peat layer were the same as of DOM in the peat profile. This suggests that the uppermost degraded peat layer is the main source of DOM. Nearly constant DOM quality through the profile furthermore indicated that DOM moving downwards through the drained sites remained largely biogeochemically unchanged. Unlike DOM concentration, DOM quality and dissolved N species distribution were similar in the two grasslands and thus unaffected by the drainage depth.
Methane production during the winter months at the drained sites was limited to the subsoil, which was quasi-permanently water saturated. The recovery of the water table in the winter months led to the production of nitrous oxide around mean water table depth at the drained sites.
The rewetted and the near-natural site had comparable DOM quantity and quality (DOC to DON ratio and aromaticity). 10 years after rewetting quasi-pristine biogeochemical conditions have been re-established under continuously water logged conditions in the former peat cut area. Only the elevated dissolved methane and ammonium concentrations reflected the former disturbance by drainage and peat extraction. Rewetting via polder technique seems to be an appropriate way to revitalize peatlands on longer timescales and to improve the water quality of downstream water bodies.
Conservation tillage practices were tested against autumn mouldboard ploughing for differences in physical properties of soil, surface runoff, subsurface drainflow and soil erosion. The study (1991-2001) was performed on a gently (2%) sloping clayey soil of southern Finland, with two replicates of the tillage treatments on 0.5 ha plots. The annual shares of surface runoff of the total flow (surface runoff + subsurface drainflow) were 8-42% for ploughing (depth 20-23 cm), 36-66% for shallow autumn stubble cultivation (depth 5-8 cm) and 36-82% for soil left untilled over winter. Surface runoff increased with decrease in the tillage intensity, and in line with the values of depressional water storage, macroporosity and saturated hydraulic conductivity. Erodibility of this gently sloping soil was at highest after autumn and spring tillage operations and decreased with time. Shallow autumn tillage produced erosion as high as mouldboard ploughing (407-1700 kg ha(-1)yr(-1)), but 48% and 12% lower erosion levels were measured from plots left untilled in autumn, covered by grass or barley residues, respectively. Eroded soil particles moved relatively freely to the subsurface drains, which carried 37-94% of the annual soil losses from the field. The study shows that even on the relatively flat clayey soils typical for southern Finland, tillage has a great influence on soil losses. The frequency of tillage needs to be reduced rather than the depth of tillage on clayey soils with poor water conductivity and structural stability if soil loss is to be diminished by conservation tillage.
Peatland drainage results in several environmental impacts such as release of greenhouse gas to the atmosphere and leaching of nutrients to watercourses. These hazardous environmental effects can partly be controlled with soil management, and different drainage and remediation practices. Grading is a new method developed for soils with low conductivity suffering from poor drainage, water logging and ice. The soil surface is graded towards the ditch to increase surface runoff and drainage. The present study compares environmental effects of peatland grading compared to traditional intense pipe drainage. Detailed measurements of hydrology, climate, leaching and gas emissions were carried out at adjacent drainage areas with grass cultivation. Additional measurements were made at plots that were abandoned, cultivated with perennial crops, and remained as pristine peatlands. The results show that the leaching of nutrients is highest from pipe drainage. Climate gas emission was considerably higher at all managed sites than from the reference pristine site. Drainage, soil hydrology and soil nutrient status seemed to control gas emissions. The gas emissions were higher than assumed for Norwegian cold conditions. The results confirm observations made on peat soils in other climatic regions. The highest emissions of CO2 were observed when the soil temperature was high and groundwater table low. The N2O emission showed a large variation with no clear pattern. However, at some locations it peaked after a dry period when NO3–N was leached. More CH4 was emitted from the intensively drained site than the graded site, but more CO2 was emitted from the graded site. The difference in leaching and emission properties is partly due to differences in near surface hydrology. At grade sites, a faster runoff response to rainfall occur probably due to shallow throughfall or overland flow which provides better drainage. The abandoned peat field no longer in cultivation continued to leach greenhouse gases in a same way as the cultivated sites.
The availability of soil nitrogen determines many functions of terrestrial ecosystems, in particular, primary plant productivity, which affects both the plant yield and carbon sequestration. Climate change will lead to shifts in soil temperature and moisture; therefore, to create a more accurate forecast of ecosystem sustainability, it is important to understand how these indicators control nitrogen mineralization in soils. We studied the effect of temperature and moisture on the net ammonification and net nitrification processes in temperate peatlands of central Russia under 4 land-use types: regular plowing for 50 and 100 years, post-agrogenic reforestation for 50 years, and a near-pristine birch forest. During a laboratory incubation experiment, we found that net nitrogen mineralization was significant at all combinations of temperatures and moisture levels. Net nitrification was the main process for nitrogen mineralization, although net ammonification was also possible at low incubation temperatures. The highest rate of net mineralization was typical of forest peatlands, and the lowest rate was typical of arable sites, which were associated with the differences in the quantity, quality and regularity of the incoming plant litter. Despite significant differences in the rate of net nitrification between plots with different land-uses, the temperature sensitivity coefficient of this process was nearly the same for all peatlands and was close to 2; therefore, we did not find evidence of the effect of the organic matter quality on the temperature sensitivity of net nitrification. The moisture level also did not affect the temperature sensitivity of this process. In general, it was found that fluctuations in soil temperature and moisture with climate change will not cause a sharp increase in net nitrification in peatlands, which will prevent the soil from losing nitrogen with runoff or in the form of gaseous compounds, such as N2O.
When considering hydrological export pathways from drained pastoral fields, the shallow groundwater underlying the artificial drainage system may fulfil an as important role as the artificial drainage system itself. However, the important split between artificial drainage and groundwater flows at a field site is usually unknown. Consequently, the effects that the groundwater system’s redox status may have on the forms and total amounts of nitrogen (N) exported from the site cannot be confidently assessed. We addressed these deficiencies by investigating the export of various forms of N in the artificial drainage and the shallow groundwater beneath two dairy farming sites (Tatuanui, Waharoa) within the Piako River catchment in New Zealand.
Due to the very low hydraulic conductivity of the degraded peat in the saturated zone perched on a clay aquiclude, no significant water or contaminants were exported at Tatuanui via the unconfined shallow groundwater. Accordingly, artificial drainage discharge into the receiving surface collector drain was the only export pathway for N at this site. The sealed nature of the groundwater zone resulted in the accumulation of organic-N and ammonium-N in the peaty shallow saturated zone underlying the mineral soil. In contrast, the Waharoa site featured a more mobile shallow groundwater system, which on average conveyed approximately equal volumes of water offsite as the artificial drainage system.
Nitrate (NO3-N) was at both sites the predominant form of N (76 %) leached from the aerobic soil profile and discharged through the artificial drainage. As the shallow groundwater was at both sites in a reduced redox state, any NO3-N leached from the rootzone into the saturated zone was consumed. Accordingly, even the mobile shallow groundwater at Waharoa did not convey significant NO3-N. The NO3-N consumption in the reduced groundwater presumably occurred due to dissimilatory NO3-N reduction (concomitant increases in ammonium-N concentrations, with no organic material available for mineralisation in the saturated zone) and microbial denitrification (producing gaseous forms of N). The NO3-N reductions in the groundwater resulted in the average total N exports via the shallow groundwater pathway at the Waharoa site being substantially lower (31 % of the exported N) than in the artificial drainage (69 %). This is despite both pathways exporting similar water volumes. Because of the NO3-N consumption in the reduced shallow groundwater at Waharoa, over 98 % of the N exported through this pathway was either as ammonium-N or organic-N.
Increases in iron (Fe) concentration have been reported in boreal regions in recent decades, raising concerns about the fate of ecosystems along water courses. In this study, the SWAT (Soil and Water Assessment Tool) model was applied to the river Mustijoki catchment in southern Finland to determine the current state of Fe transport and to evaluate possible effects of ongoing environmental change in this agriculture-dominated catchment. The model was calibrated using five-year discharge, suspended solids, and Fe data, and validated with a three-year dataset of the same parameters. Further, the model was run with spatially downscaled and bias-corrected climate change scenario data to the year 2100 obtained using five different global climate models. The results were divided into 20-year time steps (2020-2039, 2040-2059, 2060-2079, 2080-2099) and compared against a reference modeling period (1997-2016). With present catchment characteristics of the river Mustijoki, Fe transport was shown to be related to soil erosion and suspended solids transport, driven by hydrological conditions. Arable fields, especially with steeper slopes, were identified as the most likely source of Fe loading. Climate change-induced alterations in riverine Fe transport were simulated as concentrations and as annual mass fluxes. High Fe transport season is already shifting from spring snowmelt events to autumn and winter, and this change is likely to increase in coming decades. Based on modeling results, annual peak concentration in the River Mustijoki was projected to decrease by up to 32% (from 6.2 mg L-1 to 4.2 mg L-1 in scenarios RCP4.5 and RCP8.5) in the coming 20-year period, while lowest winter concentration was projected to increase by 126% (from 1.5 mg L-1 in the reference period (1997-2016) to 3.5 mg L-1 in 2080-2099 in scenario RCP8.5. To compensate for these changes in Fe transport dynamics, water protection and land use management planning must be improved.
Global expansion of high-input annual grain crops and associated nitrogen (N) fertilizer use can have negative consequences for the environment and human health. Nitrate nitrogen (NO 3-N) leaching from fertilized annual crops can contaminate groundwater and pollute natural aquatic ecosystems and rural drinking water sources. Intermediate wheatgrass (IWG; Thinopyrum intermedium) is a perennial grass being domesticated to serve as the world's first widely available perennial grain crop. Our objective was to measure water quality variables and crop yields in order to model NO 3-N leaching beneath IWG, maize, and switchgrass under three N fertilizer treatments; low N (0 kg N ha −1), medium N (maize = 80, switchgrass and IWG = 40 kg N ha −1), and high N (maize = 160, switchgrass and IWG = 120 or 160 kg N ha −1). The switchgrass and IWG medium N treatments also included alfalfa as an intercrop. The NO 3-N concentration in soil solution 50 cm below the surface was one and two orders of magnitude lower in high N fertilized IWG compared to switchgrass and maize, respectively. Soil solution NO 3-N increased with N fertilizer in all crops. Soil water content was less at 50 and 100 cm depths in IWG compared to switchgrass and maize but was unaffected by N fertilizer treatment. Using the Denitrification and Decomposition (DNDC) model, average annual NO 3-N leaching estimates in the high N treatments were 21.7 kg N ha −1 for maize and 3.7 and 0.2 kg N ha −1 for switchgrass and IWG, respectively. Despite consistent biomass yields through time, IWG grain yields decreased with stand age at all N fertilizer treatments. Alfalfa did not persist in the IWG and switchgrass medium N treatments, thus other legumes should be tested for intercropping with perennial grain crops. Intermediate wheatgrass has great potential to provide food-quality grain and biomass while preventing NO 3-N leaching.
Elevated anthropogenic acid deposition has accelerated forest soil acidification in southern China. However, the observed responses to increased acid inputs are quite variable among different forest soils, and the reasons remain unclear. To study the causes for the different responses, soil columns taken from a young pine forest (PF) and an old evergreen broadleaved forest (BF) were applied three levels of acid addition treatments for 60 days. We found that the PF soils were quite acid-sensitive, and the high acid treatment significantly decreased soil pH at 0–20 cm soil layer while significantly increased exchangeable H⁺ at both 0–20 and 20–40 cm soil layers. Both the low and high acid treatments significantly increased exchangeable Na⁺ at 0–20 cm soil layer and Ca²⁺ and Mg²⁺ at 20–40 cm soil layer. Furthermore, the high acid treatment also significantly increased leaching losses of H⁺, Ca²⁺, Mg²⁺ and Al³⁺. In contrast, the BF soils were able to buffer both the low and high acid treatments without significantly decreasing soil pH and increasing major exchangeable cations including Al³⁺ and their leaching losses. The significant differences in soil organic matter content were found to be responsible for these different responses, as a result of significantly positive correlation between cation exchange capacity (CEC) and organic carbon in both forest soils. The BF soils had higher organic matter than the PF soils, therefore a greater CEC for consuming H⁺ and a stronger capacity for binding cations. Our results explained why the PF soil pH decreased from 4.3 to 3.8, while the BF soil pH did not change significantly over the last 16 years, and highlighted the important roles of soil organic matter in acid buffering and retaining of major cations, especially for Al³⁺ in the very acidic forest soils in southern China.
Acid sulfate soil leachates deteriorate the aquatic ecosystems of their recipient waters around the world. In Finland, AS soils are located mainly on the coast of the Baltic Sea, where rivers and estuaries suffer from acid leachates and waters do not meet with the criteria of good water quality set by the EU. Field drainage of cultivated AS soils is attributable to leaching of acidity, but regardless of various mitigation measures, the acidity of discharge water in these areas has not decreased significantly. In order to better understand the pathways involved in the formation of acidity, the redox status of 56 Finnish AS soil fields was examined using redox potential and pH data measured down to 2 m. The findings indicated that the oxidation of soils has occurred at depths below the drainage pipes, with the median being at a depth of 1.6 m. In fields cultivated for a long time, soil texture had a stronger effect on the depth of the redox interface than the drainage method; open ditch drainage and subsurface drainage; oxidation being faster in sandy and silty soils than in clayey soils. The isostatic land uplift also seems to affect the depth of the redox interface in the long run. Most of the studied fields had been cultivated for at least 30 years prior to the study. However, the pH values of the soils were still very low, probably due to actual and retained acidity. The prevention of oxidation of sulfidic materials in subsoils is important, but measures for neutralizing the acidity are needed. Without them it seems that the leaching of acidity will continue and may decrease only slowly. However, severe droughts during summers and the reclamation of unripe AS soils for any purpose will increase the leaching of acidity.
Wetlands are commonly used to treat phosphorus from the effluent of municipal wastewater plants after conventional treatment and wastewater from various diffuse sources, with good results. The long term phosphorous (P) retention capacity of wetland treatment systems is a key research question. This study examined phosphorus retention in wetland (peat) soil columns in order to clarify the role of aluminium (Al) and iron (Fe) concentrations in wastewater on P removal. Since Al and Fe in wastewater could be expected to increase P uptake by increasing peat sorption capacity, laboratory flow-through column experiments were run for almost 700 days in conditions replicating the natural conditions in treatment wetlands. The study set comprised 18 peat columns and five water types from different origins (municipal wastewater, peat extraction runoff, distilled water with phosphate solutions containing 0.1 or 0.4 mg PO43− L−1, and pure distilled water). To study retention of sudden P peak concentrations, a high P peak was injected into the columns after about 500 days of wastewater loading. The results clearly showed that Al and Fe in input water maintained P removal in peat soils, with Al form also affecting retention processes, and P saturation did not occur. Therefore constructed wetlands can in some cases be safely used without the risk of P saturation. Furthermore, in the high P peak test, the additional P was successfully retained in columns with accumulated metals, showing that artificial addition of Al can be used to increase P retention capacity in peat soils with low sorption capacity.
The use of nitrogen (N) is of high interest due to its importance for food production, climate change and water quality. A comparison of N loss from agricultural areas to water in the Nordic-Baltic countries showed that the highest losses occurred in Norway. The objective of this paper was to identify temporal and spatial patterns in N concentrations in agricultural streams and to quantify the effect of production systems and agricultural management on N loss. The study includes monitoring data obtained from ten agricultural catchments (65-2830 ha), two agricultural fields (4-6 ha) and one forested catchment (19 ha). All arable areas were artificially tile drained with 8-10 m spacing and at a depth of 80-100 cm. The results showed that for all production systems average N concentrations in subsurface drainage were 2-4 times higher than in surface runoff. The average N balances for the monitored catchments varied from -12 to 132 kg ha(-1) yr(-1), but six of the catchments showed average N balances below 65 kg ha(-1) yr(-1) at which level N leaching may not be affected by increased N balance. However, N balances from single fields within the catchments varied largely, especially for areas with manure application. Seasonal variation in TN concentrations was higher in the streams in areas dominated by cereal production compared to grassland areas with the highest concentrations in May-June and September-December. Based on this study it is suggested that a strategy to even out manure application within the catchments with high livestock density should be developed. For areas with cereals, mitigation method should focus on reducing soil mineral N in spring and autumn.
It is suggested that catch crops be grown to reduce phosphorus (P) losses. However, after exposure to freezing–thawing cycles (FTCs), catch crop material can become a source of P losses to waters in moderately cold climates. This study screened potential P leaching from intact plant material of eight catch crop species: chicory (Cichorium intybus L.), cocksfoot (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), red clover (Trifolium pratense L.), phacelia (Phacelia tanacetifolia L.), white mustard (Sinapis alba L.), oilseed radish (Raphanus
sativus L. oleiformis) and white radish (R. longipinnatus). The catch crops were grown in six field experiments on clay soils, where soil lysimeters (0.25 m deep) with intact crops were extracted in autumn and used for leaching experiments before and after seven FTCs in the laboratory. The eight catch crops did not reduce P leaching before FTCs. After FTCs, leachate total-P concentrations from ryegrass, oilseed radish and red clover lysimeters were significantly (p = 0.0022) higher than those from the other species and the control without a catch crop. FTCs significantly (p = 0.0064) altered total-P concentration and the proportions of different forms of P. There was a significant increase in total-P concentration in leachate from ryegrass (p = 0.0008) and oilseed radish (p = 0.02). Thus the potential risk of P leaching from ryegrass and oilseed radish material after FTCs must be considered, since they are commonly grown as nitrogen catch crops in the Nordic countries. Moreover, the roots of the tested catch crops contained 7–86 % total-P, which is important when evaluating P leaching risks.
The leaching of sulfur ( S) and metals (Al, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Ni, Zn) from an acid sulfate soil ( ASS) area in western Finland was determined on the basis of hydrochemical analyses (ICP-MS) of water samples collected monthly for 3 years from the stream draining that area. The average annual amount of leaching was as follows (kg/ha. year): S ( 633), Ca ( 281), Mg ( 199), Al ( 54), K ( 54), Mn ( 35), Fe (5.6), Zn ( 1.7), Ni (0.84), Co (0.79), Cu (0.070), Cd (0.0068). These high values are due to extensive oxidation of metal sulfides and weathering of minerals in the ASS pro. le. Calculations showed that other S inputs such as deposition and fertiliser use, and S outputs such as degassing and plant removal, are insignificant in comparison with current leaching losses. Before the area was artificially drained, the leaching losses of S from the study area must have been very small; otherwise, the S residual in the soil would have been depleted a long time ago. With current drainage practices, the leachable soil S residual will be halved in roughly 30 years, after which the S and metal loads of the drainage will have decreased. However, more time is needed before the concentrations will have decreased to an environmentally acceptable level, unless environmentally friendly measures are found and implemented.
The nature of dissolved organic matter in river, brook, and peat mining water in the drainage basin of the humic Kiiminkijoki River, located in an area of minerotrophic peatlands in northern Finland in the boreal region, was studied by gel filtration. Special emphasis was paid to changes in the nature of high molecular weight organic Fe-P colloids that result from peat mining. The river water is organically colored, with high organic matter and Fe concentrations. High apparent molecular weight (HAMW) organic colloids are important for the transport of Fe and P in the basin. The gel filtration data suggest that the DOM in the water consist mainly of fulvic acids (FA), although humic acids (HA) are also important. The proportion of dissolved organic C (DOC) and Fe in the HAMW organic colloids increases with increasing DOC and iron concentrations in the river water. The apparent molecular weight of the DOM is higher than in the lakes in the area of ombrotrophic peatlands in southern Finland. Color in this humic water increases with DOC and Fe concentrations. The effect of Fe on color values can be seen in filtered (<1.2 μm) river water and in all the gel filtration fractions. The results indicate an increase in the mobilization of HAMW organic Fe-P colloids in the peatlands of the area following drainage and peat mining. The average ratio of Fe to DOC in the HAMW organic fraction is higher in the peat mining water than in the Keihasoja brook in a natural peaty area. It is possible that the Fe to DOC ratio in these colloids transported in the river increases following drainage and peat mining, especially under low flow conditions in summer. This may lead to gradual changes in the detritus food webs of the river ecosystem.
The acid-base buffer characteristics of fulvic acid (FA) and barium fulvate (BaFA) were analyzed. Each share of the sample
or model agents (phthalic acid and salicylic acid) were separately mixed into a series of shares of dilute solutions of HCl
or NaOH with a series of concentration. The original pH values of the solutions were arranged from 2 to 13. Final balanced
pH of each share was measured. The pH changes show that FA and BaFA possess buffer ability, whereas the model agents do not.
The tendency of balanced pH values was 5.4 for FA and 7.4 for BaFA, whereas the original pH was 4.0∼8.5; balanced pH changed
little. At room temperature, the maximum buffer capacities were as follows: 18.11 mmol hydroxyl per gram FA, 11.25 mmol hydroxyl
per gram BaFA, 1.19 mmol proton per gram FA, and 1.45 mmol proton per gram BaFA. Mathematics analysis shows that logarithm
of buffer capacities of FA and BaFA is linearly dependent on original pH. Compared with BaFA and model agents, it is concluded
that FA buffer capacity against hydroxyl relies not only on its acidic groups, BaFA buffer capacity against hydroxyl does
not rely on its acidic groups, and FA buffer capacity against proton is not related with its carboxyl and phenolic hydroxyl
group. The pH values of FA-water solutions with different concentrations from 1 to 10 grams per liter were measured. Their
pH values were slightly affected by its concentration. Thus, FA possesses a much stronger buffer ability against water dilution
than common buffer agent. All the pH values of FA water solutions were very nearby 5.4, just the same as the balanced pH tendency
for adding FA.
Tile drainage shortens the residence time of water in the soil and may therefore aggravate the diffuse pollution of adjacent surface water bodies. To assess the environmental impacts of tile drainage on surface water bodies, it is important to assess how the drainage discharge and its solute signal translate from the frequently studied plot scale to the catchment scale. We used results from the automated hydrograph separation method ‘recursive digital filter’ in combination with a two-component mixing model to quantify the role of the different flow components and flow paths for the nitrate-nitrogen losses at three different scales – collector drain outlet (4.2 ha), ditch (179 ha) and brook catchment (15.5 km2) – in a pleistocene lowland area in North-Eastern Germany. Measured and modelled NO3-N concentrations of three 6-months winter seasons agreed reasonably well. At the tile drainage plot, the fast flow component was responsible for 63–91% of the total simulated nitrate-nitrogen losses. The stated ranges were derived from all accepted model runs. This flow component was interpreted as a fast component bearing nitrate from the nutrient-enriched topsoil. Tile drainage itself delivered 89–95% of the total nitrate losses in the ditch catchment. In the brook catchment, at most 25% of the area was responsible for 54–85% of the NO3-N losses. Although the mixing model is limited by the assumption of constant component concentrations and conservative behaviour of the solutes, it has shown to be a useful tool for hydrochemical studies. Overall, the results emphasise the importance of tile drainage for the catchments’ hydrochemistry and its environmental impact on the larger scale. Consequently, it will be difficult to significantly reduce diffuse pollution in an artificially drained lowland landscape on the catchment scale without addressing the issue of tile drainage. As a next step for model validation, other solutes such as sulphate and chloride could be added to reduce the uncertainty, and grassland should be explicitly included into the mixing model.
This study introduces a prototype model for evaluating policies to abate agricultural nutrients in the Baltic Sea from a Finnish national point of view. The stochastic simulation model integrates nutrient dynamics of nitrogen and phosphorus in the sea basins adjoining the Finnish coast, nutrient loads from land and other sources, benefits from nutrient abatement (in the form of recreation and other ecosystem services) and the costs of agricultural abatement activities. The aim of this study is to present the overall structure of the model and to demonstrate its potential using preliminary parameters. The model is made flexible for further improvements in all of its ecological and economic components. Results of a sensitivity analysis suggest that investments in reducing the nutrient runoff from arable land in Finland would become profitable only if Finland’s neighbors in the northern Baltic committed themselves to similar reductions. Environmental investments for improving water quality yield the highest returns for the Bothnian Bay and the Gulf of Finland, and smaller returns for the Bothnian Sea. In the Bothnian Bay, the abatement activities become profitable because the riverine loads from Finland represent a high proportion of the total nutrient loads. In the Gulf of Finland, this proportion is low, but the size of the coastal population benefiting from improved water quality is high.
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Impacts on Runoff Water Quality in a Northern New York (USA) Tile-Drained Maize
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