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We used a process-based hydrological model SUSI to improve guidelines for ditch network maintenance (DNM) operations on drained peatland forests. SUSI takes daily weather data, ditch depth, strip width, peat properties, and forest stand characteristics as input and calculates daily water table depth (WTD) at different distances from ditch. The study focuses on Scots pine ( L.) dominated stands which are the most common subjects of DNM. Based on a literature survey, and consideration of the tradeoffs between forest growth and detrimental environmental impacts, long term median JulyâAugust WTD of 0.35 m was chosen as a target WTD. The results showed that ditch depths required to reach such WTD depends strongly on climatic locations, stand volume, ditch spacing, and peat thickness and type. In typical ditch cleaning areas in Finland with parallel ditches placed about 40 m apart and tree stand volumes exceeding 45 m ha, 0.3â0.8 m deep ditches were generally sufficient to lower WTD to the targeted depth of 0.35 m. These are significantly shallower ditch depths than generally recommended in operational forestry. The main collector ditch should be naturally somewhat deeper to permit water outflow. Our study brings a firmer basis on environmentally sound forestry on drained peatlands.Pinus sylvestris3â1

In Finland nearly 6 million hectares of peatlands are drained for forestry purposes. Ditch network maintenance in the drained peatlands, i.e. cleaning old ditches or digging complementary ditches, deteriorates surface water quality by increasing the export of dissolved elements and suspended solids (SS). Effect of ditch network maintenance on the export of SS, dissolved organic carbon (DOC), and dissolved nitrogen (N), phosphorous (P), iron (Fe), aluminum (Al) and manganese (Mn) was studied in nine pairs of treated and control (no maintenance) catchments located in southern and central Finland. In this study we extended the paired catchment approach by combining data from several catchments and identifying the treatment effect on SS and element loads from the entire dataset. Following the method of Laurén et al. (2009) we identified how uncertainty in correlation between treatment and control catchments during pre-treatment period is reflected in the estimated treatment effect on SS and element loads. In the experiment, the export of SS increased significantly for the four year study period following the ditch network maintenance and Al export increased for one year. The export of N, P and Fe was not significantly changed and DOC and Mn export decreased after the ditch maintenance operation.

Our current knowledge of the P retention efficiency of peatland buffer zone areas used to reduce sediment and nutrient leaching from forestry areas is insufficient. Especially the role of P sorption by soil in buffer zones needs closer examination as there is considerable variation in the efficiency of P retention. Six sites in southern Finland were chosen for the study. The buffer zone areas varied between 0.1â4.9% of the catchment area. A total of 10 kg of solute POâP was added to the inflow of the buffer zone areas and the concentrations of POâP in inflow and outflow were measured for 2â4 years. P retention characteristics of the surface peat were determined with sorption-desorption isotherms before and after POâP addition and the effective buffer zone area over which the added P was spread was determined from soil water samples. P retention in the two largest buffer zone areas was complete (100% retention), and the third largest buffer retained 94%. Retention in the three smallest buffer zones was 24%, 95% and 95% of the added P. As a result of P addition reduction in peat P retention capacity was detected in three out of four cases. The effective buffer zone area varied from 67% to 100% of the total buffer zone area. Factors contributing to efficient P retention were large buffer size and low hydrological load whereas high hydrological load combined with the formation of preferential flow paths, especially during early spring or late autumn was disadvantageous. High P retention capacity in peat contributed to the sustainability of P retention. The study showed that even relatively small buffer zone areas are able to efficiently reduce P load.444

Fertilization of drained peatland forests with wood ash and different commercial phosphorus fertilizers (calcium phosphates) generally give similar stand growth responses. However, it has been shown that use of calcium phosphate fertilizers generally lead to highly increased P release to recipient water courses. On the other hand, no corresponding release has been reported after ash fertilization. Soil samples from the surface peats from a nutrient poor and a fertile drained peatland site were collected before and 1â4 years after application of five different types of ash products. The changes over time in the different chemical forms of P in the substrate were studied. The results indicated that the reason for the low liability to leaching of ash fertilizers was that significant amounts of P are adsorbed by Al and Fe during weathering of the ash fertilizers. However, further studies are needed to clarify whether the adsorption of P occurs with the Al and Fe of the ash or the native Al and Fe compounds present in soil before ash fertilization.

In 1995â2001, the efficiency of riparian buffer zone areas to reduce the concentrations of suspended solids in discharge from peatlands drained for forestry purposes was studied at 7 locations in south-central Finland. The two largest buffer zones reduced the concentrations of suspended solids by > 70%. The efficiency of the three medium-sized buffer zones to reduce through-flow sediment concentrations was 50â60%, but no reduction occurred at the smallest two buffer areas. Thus, the capacity of buffer zones to reduce sediment concentrations was strongly related to their size. However, significant correlations were also found between reduction capacity and inflow water sediment concentrations, although the correlations at the two smallest buffer zones were low. The use of buffer zones in reducing sediment load from peatlands drained for forestry purposes is recommended, but relatively large areas for efficient removal capacity are needed.

Soil samples from 15 eutrophic, 26 herb-rich, 15 tall-sedge, and 11 low-sedge drained peatland sites were analysed for easily soluble and aluminum, iron, and calcium bound phosphorus (P) using the Chang and Jackson sequential fractionation method. Compared to earlier investigations, where only total and easily soluble P contents (e.g. NH4OAc or dilute H2SO4 extractable P) in peat have been analysed, significantly higher differences between sites were observed. The eutrophic sites were characterized by four to six-fold greater Ca-bound organic P and two to three-fold greater Ca-bound inorganic P contents than on the other three site type groups, whereas the average Al-bound inorganic P content of the eutrophic sites was only one-third of that at the other site types. Substantial differences between sites were also observed for Fe-bound inorganic P, i.e. two to four-fold greater Fe-P contents were measured at the herb-rich sites compared with the other three site type groups. The stand volume growth in the 67 studied drained peatland sites correlated significantly with Al-bound organic P and Fe-bound inorganic and organic P. The study showed that a detailed fractionation and discrimination of different forms of soil P is important in increasing the understanding of the relationship between P availability and vegetation community types and stand growth on drained peatlands.

The effect of clear-cutting on the concentrations of dissolved organic carbon (DOC), organic nitrogen (DON), NH4+, NO3â, and P in outflow water from three productive, Norway spruce dominated drained peatlands (RCC, VCC-1, VCC-2) were studied. Changes in runoff and transport loads (concentration x runoff) at two of the catchments during the frost-free period are also presented. Approximately 40% of the area was cut at RCC and VCC-2, and 72% at VCC-1. The volume removed was 250 m3 haâ1 at RCC, 259 m3 haâ1 at VCC-1, and for VCC-2, 317 m3 haâ1. The mean annual increase in outflow concentrations of DOC during the first four years after clear-cutting was 9.0 mg lâ1 at RCC, 22.8 mg lâ1 at VCC-1 and 8.4 mg lâ1 at VCC-2. Corresponding increases in the forms of nitrogen were: 0.23, 0.51 and 0.16 mg DON lâ1; 0.06, 0.31 and 0.04 mg NH4+-N lâ1; and 0.05, 0.12 and 0.22 mg NO3â-N lâ1. Clear-cutting did not significantly (p > 0.05) increase P concentrations. The increase in non-frost season runoff over the first three years after clear-cutting was 107 mm at RCC and 207 mm at VCC-1. The export loads of DOC during the non-frost season increased by 80 kg haâ1 at RCC and by 184 kg haâ1 at VCC-1 over the first three years. Corresponding increases for the other studied solutes were: 1.78 and 3.98 kg DON haâ1; 0.39 and 1.49 kg NH4+-N haâ1; 0.45 and 0.48 kg NO3â-N haâ1, and 0.09 and 0.06 kg P haâ1. The study demonstrated that clear-cutting may significantly increase the export of DOC and different forms of nitrogen from drained productive peatlands while only small increases in phosphorus export may occur.

Dry mass and nutrient (N, P, K, Ca, Mg, B) contents of field layer vegetation and a combination of bottom layer vegetation and litter (referred to as bottom/litter layer in the text) were studied one year before and three years after fertilization (NPK and PK) on a drained low-shrub pine bog in eastern Finland. The results of an earlier study on the tree layer were combined with those of this study in order to estimate the changes caused by fertilization in the total plant biomass and litter. Before fertilization the average dry mass of the field and bottom/litter layers was 8,400 kg ha and 7,650 kg ha respectively. The above-ground parts accounted for 25% of the total field layer biomass. The dry mass of the field and bottom/litter layers together was < 20% of the dry mass accumulated in the total plant biomass and litter. The corresponding figures for N, P, K, Ca, Mg and B were 44%, 38%, 30%, 38%, 31% and 17%, respectively. Fertilization did not significantly affect the dry mass of either the field layer vegetation or the bottom/litter layer. 33% of the applied P was accumulated in the total plant biomass and litter on the PK-fertilized plots, and 25% on the NPK-fertilized plots. For the other elements, the proportions on the PK-fertilized plots were K 31%, Ca 6%, Mg 11% and B 13%. On the NPK-fertilized plots, the corresponding figures were N 62%, K 32%, Ca 6%, Mg 9% and B 13%. Except for B and K, the accumulation of fertilizer nutrients in the understorey vegetation and litter was of the same magnitude or greater than the uptake by the tree layer.-1-1,

Ditch network maintenance promotes forest growth in drained peatland forests but increases nutrient and sediment loads, which are detrimental to water quality. Society needs to balance the harvest revenue from improved forest growth against deteriorating water quality. We examine socially optimal even-aged forest management in drained peatlands when harvesting and ditch network maintenance cause nutrient and sediment loading. The means to reduce loading include establishing overland flow fields and abstaining from ditch network maintenance. We characterize this choice analytically in a rotation framework and examine, in a numerical model, the key factors affecting the choice of forest management and water protection measures. We choose a drained peatland forest site located in northeastern Finland in the vicinity of ecologically vulnerable forest headwater streams. On the given drained forest site, we find a set of parameters under which implementing ditch network maintenance is privately but not socially optimal. Key words: ditch network maintenance, Faustmann rotation model, nutrient load, overland flow field, sediment load. L'entretien du reseau de canaux favorise la croissance de la foret dans les tourbieres arborees drainees mais augmente la charge de nutriments et de sediments qui sont nefastes pour la qualite de l'eau. La societe doit chercher un equilibre entre les revenus de la recolte generes par l'amelioration de la croissance de la foret et la deterioration de la qualite de l'eau. Nous avons etudie l'amenagement forestier equienne socialement optimal dans les tourbieres drainees lorsque la recolte et l'entretien du reseau de canaux entrainent un apport de nutriments et de sediments. Les moyens de reduire cet apport incluent l'etablissement de champs de ruissellement et l'abstention de l'entretien du reseau de canaux. Nous avons caracterise ce choix de facon analytique dans le cadre d'une rotation et nous avons examine avec un modele numerique les facteurs cles qui influencent le choix des mesures d'amenagement forestier et de protection de l'eau. Nous avons choisi une tourbiere arboree drainee situee dans le nord-est de la Finlande, a proximite de ruisseaux forestiers de tete ecologiquement vulnerables. Dans la station forestiere drainee qui a ete choisie, nous avons trouve un ensemble de parametres selon lesquels l'entretien du reseau de canaux est optimal d'un point de vue prive mais non d'un point de vue social. [Traduit par la Redaction] Mots-cles : entretien du reseau de canaux, modele de rotation de Faustmann, charge de nutriments, champ de ruissellement, charge de sediments., 1. Introduction Pristine peatlands are wet forest sites where high soil water levels are a limiting factor for tree growth. To increase commercial tree growth, drainage is generally needed to [...]

Reducing the strain on water bodies caused by sediment loads released after ditch network maintenance (DNM) is addressed in operational peatland forestry by implementing sediment control structures in ditches. This study evaluates computationally alternative sediment control scenarios in a 5.2 ha deep peat site in eastern Finland. Coupled to a distributed hydrological model, peat erosion and transport in the ditches were simulated for the first year after DNM with 15 scenarios consisting of individual structures (e.g., sedimentation ponds) and their combinations. One scenario represented the prevailing conditions with a V-notch weir at the catchment outlet. All scenarios were evaluated against a baseline scenario in which no structures affected the catchment sediment processes. The results suggested that bed erosion can be efficiently prevented with breaks in cleaning and structures ponding water. It was proven less efficient to trap already eroded material with sedimentation ponds and pits. The structures raising ditch water level had limited effects on water table levels in the strips between ditches, plausibly not impairing tree growth. The process-based modeling presented here provided a yet unexplored approach to comprehensively evaluating alternatives for sediment control, which is highly needed to address the gap between existing scientific knowledge and operational peatland forestry practices. Key words: erosion modeling, forestry, hydrological modeling, peatland drainage, water protection. La reduction de la pression sur les plans d'eau causee par les charges de sediments liberes a la suite de travaux d'entretien des reseaux de fosses est realisee en pratique dans les tourbieres forestieres par la mise en place de structures de controle dans les fosses. Cette etude evalue au moyen de simulations par ordinateur des scenarios alternatifs de controle des sediments dans une tourbiere profonde de 5,2 ha situee dans l'est de la Finlande. Couplee a un modele hydrologique reparti, l'erosion et le transport de la tourbe dans les fosses ont ete simules pendant la premiere annee suivant des travaux d'entretien avec 15 scenarios constitues de structures individuelles (p. ex., des bassins de decantation) et de leurs combinaisons. Un scenario representait les conditions existantes avec un deversoir a echancrure triangulaire a la sortie du bassin hydrographique. Tous les scenarios ont ete evalues par rapport a un scenario de base dans lequel aucune structure n'influencait le transport des sediments dans le bassin. Les resultats indiquent qu'on peut efficacement prevenir l'erosion du lit avec des structure qui retiennent l'eau et en laissant certaines sections des fosses non nettoyer. Les basins et les fosses de sedimentation se sont averes moins efficaces pour retenir le materiel deja erode. Les structures qui elevent le niveau de l'eau dans les fosses avaient peu d'effet sur le niveau de la nappe phreatique dans les bandes entre les fosses et n'avaient vraisemblablement pas d'impact negatif sur la croissance des arbres. La modelisation fondee sur les processus qui est presentee ici fournit une approche encore inexploree pour evaluer de facon exhaustive les alternatives pour le controle des sediments, ce qui est absolument necessaire pour combler l'ecart entre les connaissances scientifiques actuelles et les pratiques utilisees dans les tourbieres forestieres. [Traduit par la Redaction] Mots-cles : modelisation de l'erosion, foresterie, modelisation hydrologique, drainage des tourbieres, protection de l'eau., 1. Introduction Increased suspended sediment (SS) loads originating from peatland drainage are widely recognized (e.g., Robinson and Blyth 1982; Prevost et al. 1999; Pavey et al. 2007), and the resulting [...]