Hannu Marttila

Effect of soil properties on peat erosion and suspended sediment delivery in drained peatlands

Erosion from peat extraction areas is known to cause siltation of water courses and poor water quality. However, the main soil parameters affecting peat erosion and suspended sediment (SS) yields from different catchments are not well understood. This paper used peat properties (degree of humification, peat type, ash content, porosity, moisture content, bulk density, and shear strength) and novel erosion threshold measurements from intact soil cores to explain peat erodibility and spatial variations in SS concentrations (SSCs) and SS loads (SSLs) at 20 Finnish peat extraction sites. The erosion threshold measurements suggested that critical shear stresses for particle entrainment decrease with increasing degree of humification (von Post scale) and are significantly lower in well-decomposed peat than in slightly or moderately decomposed peat. Two critical shear stresses were obtained from moderately decomposed peat samples, indicating a degree of surface armoring by coarse peat fibers. Monitored long-term average SSC was highest at study sites with well-decomposed peat, while very fine-grained mineral subsoil explained some of the highest long-term SSC in areas where drainage ditches penetrated below the upper peat layer. Average SSL (kg d−1) at the study sites was best explained (R2 = 0.89) by average discharge and surface peat decomposition level. Overall, this study provides new knowledge on peat erosion and critical shear stresses that can be used in water conservation and sediment management practices for cutover peatlands and other similar land uses.

Water‐table‐dependent hydrological changes following peatland forestry drainage and restoration: Analysis of restoration success

A before-after-control approach was used to analyze the impact of peatland restoration on hydrology, based on high temporal resolution water-table (WT) data from 43 boreal peatlands representative of a south-boreal to north-boreal climate gradient. During the study, 24 forestry drained sites were restored and 19 pristine peatlands used as control sites. Different approaches were developed and used to analyze WT changes (mean WT position, WT fluctuation, WT hydrograph, recession, and storage characteristics). Restoration increased WT in most cases but particularly in spruce mires, followed by pine mires and fens. Before restoration, the WT fluctuation (WTF) was large, indicating peat temporary storage gain (SG). After restoration, the WT hydrograph recession limb slopes and SG coefficients (Rc) declined significantly. Drainage or restoration did not significantly affect mean diurnal WT fluctuations, used here as a proxy for evapotranspiration. Overall, the changes in WT characteristics following restoration indicated creation of favorable hydrological conditions for recovery of functional peatland ecosystems in previously degraded peatland sites. This was supported by calculation of bryophyte species abundance thresholds for WT. These results can be used to optimize restoration efforts in different peatland systems and as a qualitative conceptual basis for future restoration operations.

Restoration of nutrient-rich forestry-drained peatlands poses a risk for high exports of dissolved organic carbon, nitrogen, and phosphorus

Restoration impact of forestry-drained peatlands on runoff water quality and dissolved organic carbon (DOC) and nutrient export was studied. Eight catchments were included: three mesotrophic (one undrained control, two treatments), two ombrotrophic (one drained control, one treatment) and three oligotrophic catchments (one undrained control, two treatments). Three calibration years and four post-restoration years were included in the data from seven catchments, for which runoff was recorded. For one mesotrophic treatment catchment only one year of pre-restoration and two years of post-restoration water quality data is reported. Restoration was done by filling in and damming the ditches. Water samples were collected monthly-biweekly during the snow-free period; runoff was recorded continuously during the same period. Water quality was estimated for winter using ratios derived from external data. Runoff for non-recorded periods were estimated using the FEMMA model. A high impact on DOC, nitrogen (N) and phosphorus (P) was observed in the mesotrophic catchments, and mostly no significant impact in the nutrient-poor catchments. The DOC load from one catchment exceeded 1000kg (restored-ha)-1 in the first year; increase of DOC concentration from 50 to 250mgl-1 was observed in the other mesotrophic treatment catchment. Impact on total nitrogen export of over 30kg (restored-ha)-1 was observed in one fertile catchment during the first year. An impact of over 5kg (restored-ha)-1 on ammonium export was observed in one year in the mesotrophic catchment. Impact on P export from the mesotrophic catchment was nearly 5kg P (restored-ha)-1 in the first year. The results imply that restoration of nutrient-rich forestry-drained peatlands poses significant risk for at least short term elevated loads degrading the water quality in receiving water bodies. Restoration of nutrient-poor peatlands poses a minor risk in comparison. Research is needed regarding the factors behind these risks and how to mitigate them.

Changes in Pore Water Quality After Peatland Restoration: Assessment of a Large‐Scale, Replicated Before‐After‐Control‐Impact Study in Finland

Drainage is known to affect peatland natural hydrology and water quality, but peatland restoration is considered to ameliorate peatland degradation. Using a replicated BACIPS (Before-After-Control-Impact Paired Series) design, we investigated 24 peatlands, all drained for forestry and subsequently restored, and 19 pristine control boreal peatlands with high temporal and spatial resolution data on hydroclimate and pore water quality. In drained conditions, total nitrogen (Ntot), total phosphorus (Ptot), and dissolved organic carbon (DOC) in pore water were several-fold higher than observed at pristine control sites, highlighting the impacts of long-term drainage on pore water quality. In general, pore water DOC and Ntot decreased after restoration measures but still remained significantly higher than at pristine control sites, indicating long time lags in restoration effects. Different peatland classes and trophic levels (vegetation gradient) responded differently to restoration, primarily due to altered hydrology and varying acidity levels. Sites that were hydrologically overrestored (inundated) showed higher Ptot, Ntot, and DOC than well-restored or insufficiently restored sites, indicating the need to optimize natural-like hydrological regimes when restoring peatlands drained for forestry. Rich fens (median pH 6.2–6.6) showed lower pore water Ptot, Ntot, and DOC than intermediate and poor peats (pH 4.0–4.6) both before and after restoration. Nutrients and DOC in pore water increased in the first year postrestoration but decreased thereafter. The most important variables related to pore water quality were trophic level, peatland class, water table level, and soil and air temperature.

Transport of particle-associated elements in two agriculture-dominated boreal river systems

Transport of particulate pollutants in fluvial systems can contribute greatly to total loads. Understanding transport mechanics under different hydrological conditions is key in successful load estimation. This study analysed trace elements and physico-chemical parameters in time-integrated suspended sediment samples, together with dissolved and total concentrations of pollutants, along two agriculture- and peatland-dominated boreal river systems. The samples were taken in a spatially and temporally comprehensive sampling programme during the ice-free seasons of 2010 and 2011. The hydrochemistry and transport of particle-bound elements in the rivers were strongly linked to intense land use and acid sulphate soils in the catchment area, with arable, pasture and peat areas in particular being main diffuse sources. There were significant seasonal and temporal variations in dissolved and particulate fluxes, but spatial variations were small. Continuous measurements of EC, turbidity and discharge proved to be an accurate indicator of dissolved and particulate fluxes. Overall, the results show that transport of particle-bound elements makes a major contribution to total transport fluxes in agriculture-dominated boreal rivers.

Use of Turbidity Measurements to Estimate Suspended Solids and Nutrient Loads from Peatland Forestry Drainage

AbstractContinuous determination of suspended solids (SS) by turbidity measurements in drained peatland is expanding, increasing the demand for reliable calibration data for load calculations. Turbidity was used to estimate SS (n=333) and particulate nutrient loads (n=157) after peatland drainage for forestry in Central Finland for three study catchments. SS data from the drainage outlet correlated well with turbidity, demonstrating that turbidity can be used as an accurate measure of SS in drained peatland conditions. Measurement error was found to be approximately 8% (p<0.01). The proportion of organic and inorganic fractions in SS seemed to affect calibration. Total phosphorus, total nitrogen, and particulate phosphorus showed linear dependency on turbidity values because a fraction of these nutrients occurs in particulate form or adsorbed to organic matter. Regressions during snowmelt periods were markedly different from those in other periods that were related to changes in the dissolved/total nutrie...

Defining the natural flow regimes of boreal rivers: relationship with benthic macroinvertebrate communities

Despite the fundamental role of river flow in determining the structure and function of lotic ecosystems, few studies have directly related features of the natural flow regime to variation in stream invertebrate assemblage composition. We classified 240 near-pristine, snowmelt-dominated Finnish streams into hydrological river types. We assessed the relationship of these types with benthic macroinvertebrate assemblage structure and examined the relative importance of hydrological variables, local-habitat variables, and geographical location in predicting variation in assemblage structure. We used a hydrological model to obtain site-specific daily discharges for a 30-y period (1981–2010) and calculated 223 flow indices based on flow index modeling tools. We used a combination of principal component and cluster analysis to classify the sites into 6 distinct hydrological types that were separated mainly by geographical location and catchment-size-related factors. Nonmetric multidimensional scaling and multiresponse permutation procedure showed that macroinvertebrate assemblage structure differed significantly among the hydrological types, but the associated A-statistic indicated wide variation among sites within type. Redundancy analysis indicated that assemblage structure was related more closely to hydrological variables than to local-habitat and spatial variables. The role of hydrology was confirmed further by functional trait structure that showed close relationships to hydrological variables in three-table ordination (RLQ) and fourth-corner analyses. Traits representing organism size and microhabitat preference were correlated most closely with hydrological variables describing variability or seasonality of flows. Our study highlights the role of hydrology in structuring stream assemblages in seasonal, snowmelt-dominated river systems. Modeling hydrological variables in combination with species distribution models may provide a tool for predicting future changes in species distributions in stream ecosystems.

Effect and design of an underminer structure

Wooden debris structures are commonly used in stream restoration to alter sediment transport and flow distributions to improve fish habitats in degraded streams. Various wooden structures were tested in a laboratory flume to determine their ability to change flow patterns, resulting in local scour. A parametric study was made to predict scour hole depth. The results indicate that the underminer structure should cover the full channel width and divert the whole flow below the structure. Maximum scour depth was obtained with a single structure perpendicular to the flow direction and overall scour depth was governed by structural height and sediment particle size distribution. With increasing structure angle with respect to flow, the area and volume of the scour hole increase, whereas the scouring depth decreases. Coarser sediment size reduces scour depth for both single and consecutive structures. The optimum underminer spacing ratio was found to be 2 to 3 times the channel width.

Does transpiration from invasive stream side willows dominate low-flow conditions? An investigation using hydrometric and isotopic methods in a headwater catchment

12 Understanding seasonal partitioning of water in riparian areas is important for assessing how 13 vegetation affects water resources. A combined hydrological-isotopic field study was conducted 14 within a headwater catchment to explore the dynamics of stream discharge and the effect of riparian 15 evapotranspiration (ET) on summer low flow conditions. In addition to collection of meteorological 16 data and depth to unconfined groundwater, stream flows were measured at three locations along the 17 length of the river. Isotope ratios of local precipitation, stream water, groundwater, and willow 18 xylem water were used to estimate pathways and sources of water used by vegetation. Using 19 meteorological variables, leaf area index and stand area measurements, willow transpiration (T) was 20 estimated using the Penman-Monteith method. Combining the data from hydrometric, isotope, and 21 vegetation ET analysis revealed that water abstraction by stream-side willows peaked to 5.6 22 mm/day and had a distinct impact on summer low-flow conditions and patterns of stream discharge 23 at the daily time scale. Average annual willow transpiration was 270 mm, while average annual 24 precipitation during the study period was 1067 mm. However, willow transpiration reduced stream 25

A synthesis of the impacts of ditch network maintenance on the quantity and quality of runoff from drained boreal peatland forests

Drained peatlands are an important source of forest biomass in boreal regions and ditch network maintenance (DNM) operations may be needed to restore the drainage functions of ditches. By reviewing the available literature, as well as utilizing an existing hydrological model and analyzing the characteristics of eroded sediments, we assessed the impacts of DNM on runoff and exports of suspended solids (SS), dissolved organic carbon (DOC), nitrogen (N), and phosphorus (P). In general, DNM had minor impact on runoff and dissolved N and P, and it decreased rather than increased DOC exports. To increase the understanding of the hydrochemical impacts of DNM, future research should focus on the characteristics of SS and particulate nutrient exports. A major gap in knowledge is also the very limited regional representativeness of the available studies. High erosion risk in the ditches reaching the mineral soil below peat should be acknowledged when planning mitigation measures.