Jari Koskiaho

Retaining agricultural nutrients in constructed wetlands—experiences under boreal conditions

Constructed wetlands are among the eutrophication abatement measures for which farmers may receive public subsidies in Finland. To assess the performance of constructed wetlands under boreal conditions, we monitored the retention of total suspended solids (TSS), total P (TP), dissolved reactive phosphorus (DRP), total N (TN), nitrate+nitrate-N (NOx-N) and ammonium-N (NH4-N) for 15–26 months in three constructed wetlands located in southern Finland. Annual retentions were −5–72% for TSS, −6–67% for TP, −33–33% for DRP, −7–40% for TN, −8–38% for NOx-N and −50–57% for NH4-N. The constructed wetland with the longest water residence time (WRT) showed the best performance, retaining annually about 25 kg of TP and 300 kg of TN per hectare. In contrast, the constructed wetland with the shortest WRT functioned only occasionally and was a net source for DRP and NOx-N. In addition to the WRT, high P sorption capacity of constructed wetland soil and high input concentrations appeared to promote retention. Vegetation had a limited effect, input load being transported mostly outside the growing season. When carefully designed and located, constructed wetlands may efficiently reduce nutrient loading from agriculture.

Flow velocity retardation and sediment retention in two constructed wetland–ponds

Abstract Hydraulic properties of two constructed wetland–ponds in agricultural watersheds in southern Finland were examined by simulations with two-dimensional hydrodynamic and water quality transport models. Hydraulic efficiency was determined for the existing and hypothetical layouts of both wetlands to find out the effects of different design options. Suspended sediment retention in the wetlands was simulated with a two-dimensional model for sediment transport. Hydraulic efficiency was found to be highly improved by baffles that direct the main flow to optimally exploit the wetland acreage. Also, an elongated shape of wetland appeared beneficial; hydraulic efficiency was high regardless of the size or position of the inlet. As for suspended sediment retention, the wetland area in relation to its watershed proved to be an essential factor. According to water quality observations, the wetland which occupied 5% of its watershed area was capable of reducing the inflow of total suspended solids (TSS) concentrations during flood events by 43–72%, whereas the reduction varied between −7 and 5% in the other wetland with a corresponding ratio of 0.5%. Model simulations of the same flood events plausibly predicted the output TSS concentrations, even though with wider ranges of the reductions (26 to 74 and −13 to 43%, respectively).

Wireless in-situ Sensor Network for Agriculture and Water Monitoring on a River Basin Scale in Southern Finland: Evaluation from a Data User’s Perspective

Sensor networks are increasingly being implemented for environmental monitoring and agriculture to provide spatially accurate and continuous environmental information and (near) real-time applications. These networks provide a large amount of data which poses challenges for ensuring data quality and extracting relevant information. In the present paper we describe a river basin scale wireless sensor network for agriculture and water monitoring. The network, called SoilWeather, is unique and the first of this type in Finland. The performance of the network is assessed from the user and maintainer perspectives, concentrating on data quality, network maintenance and applications. The results showed that the SoilWeather network has been functioning in a relatively reliable way, but also that the maintenance and data quality assurance by automatic algorithms and calibration samples requires a lot of effort, especially in continuous water monitoring over large areas. We see great benefits on sensor networks enabling continuous, real-time monitoring, while data quality control and maintenance efforts highlight the need for tight collaboration between sensor and sensor network owners to decrease costs and increase the quality of the sensor data in large scale applications.

On-line measurements provide more accurate estimates of nutrient loading: a case of the Yläneenjoki river basin, southwest Finland

Automatic on-line measurement stations for water quality components and water level were equipped with dataloggers and GSM transmitters; the stations were installed at two sites in the Yläneenjoki river basin, SW Finland. Measurements during five seasons in 2006-2007 were conducted to find out whether the produced data would provide more accurate estimates of material and nutrient transport than traditional water sampling. Sensor-based monitoring estimates for transport of total suspended solids (TSS) were clearly higher (difference -6-61%), total phosphorus also higher, and that of nitrate (NO(3)-N) somewhat lower (difference (-51%-4%), as compared with manual sampling based estimates. The winter season studied here was mild i.e. winter-type which is becoming more common in Finland with the changing climate. Sensor-based monitoring proved its benefits particularly in such conditions.

Convective oxygen transport in a constructed wetland pond : Mechanism, measurements and modelling by multilayer perceptrons

Abstract The study presented here found evidence for the presence and importance of convective flows and associated oxygen transport in a constructed wetland pond in southern Finland. These flows are triggered by nightly cooling of the water at the surface, which may then become denser than the water lower down in the pond. The resulting layering (heavier water overlying less dense one) is hydromechanically unstable and—almost immediately—starts driving convective motion. This flow takes oxygen enriched water from the surface to the bottom of the wetland, where a distinct rise in oxygen saturation is recorded after some time lag. The process described can be modelled successfully by means of so-called Multilayer Perceptrons (MLPs), a class of Artificial Neural Networks. As explored in this study, these models are well suited to “learn” the mechanism of convective transport, which results in their ability to forecast oxygen saturation near the wetland bottom at a satisfactory level of accuracy.

Temporal trends in phosphorus concentrations and losses from agricultural catchments in the Nordic and Baltic countries

This paper in a uniform manner examines temporal trends in phosphorus (P) concentrations and losses from small and well-monitored agricultural catchments in the Nordic and Baltic countries. Thirty-four catchments (range 0.1–33 km2) in Norway (8), Denmark (5), Sweden (8), Finland (4), Estonia (3), Latvia (3) and Lithuania (3) were selected for the study. The time series ranged from 10 (2002–2011) to 21 years (1989–2009). The monthly P concentration and loss time series were tested for significant monotone trends (p < 0.05; two-sided test) using the partial Mann–Kendall test with stream discharge as an explanatory variable. The results show a large variation in concentrations and losses of total phosphorus (TP) among the 34 studied catchments, where the long-term mean annual losses varied from 0.09 to 7.5 kg TP ha−1. In addition, a large interannual variability in losses within catchments was found with up to a factor of 23 between years within the same catchment. Six catchments showed downward temporal trends in the TP loss time series. One upward trend in TP losses was detected in a catchment in south-west Sweden. Eight downward trends were detected in the TP concentration time series. Overall, our results show (1) a huge variability in mean P losses and concentrations among catchments, (2) a huge temporal variability in losses within catchments and (3) few detectable changes in P losses and concentrations over the study period. The results showcase the need for implementation of mitigation strategies towards reduced P losses from agricultural landscapes in the Nordic/Baltic Sea region in order to improve P water quality and ecology in surface waters.

Constructed wetlands in Finnish agricultural environments: balancing between effective water protection, multi-functionality and socio-economy / Małe sztuczne zbiorniki wodne w krajobrazie rolniczym Finlandii: ochrona jakości wody na tle wielozadaniowych funkcji tych zbiorników i aspektów socjalno-ekonomicznych

Abstract This case study summarizes the current knowledge in Finland on the efficiency of constructed wetlands to improve water quality at the same time providing multiple benefits. The efficiency is highly dependent on the wetland’s relative size compared to the upstream catchment area, and on the amount of agricultural land in the upstream catchment. The case study analyses the incentives designed to motivate landowners to construct wetlands in Finland such as the non-productive investment support and the agri-environment payment support for wetland management. Farmers think that the support system is heavy and bureaucratic, and thus the target number of new constructed wetlands is far from being met. Individual projects have been more successful in wetland construction than the official support system. General wetland plans drafted for hotspot areas is an example of enabling factors and strict eligibility rules form one of the barriers of wetland construction identified in this case study. In spite of the criticism of the current wetland incentives, a support system for wetland construction is needed. One option would be to give regional authorities more freedom to select priority areas according to e.g. River Basin Management Plans. Streszczenie Artykuł stanowi podsumowanie stanu wiedzy w Finlandii na temat wielofunkcyjności niewielkich sztucznych zbiorników wodnych, w tym szczególnie poprawy jakości wody. Efektywność takich zbiorników w ochronie wód w dużym stopniu zależy od stosunku wielkości tych akwenów do obszaru zlewni bezpośredniej i wielkości powierzchni użytkowanej przez rolnictwo w tej zlewni. Badania obejmowały analizę takich czynników, jak pomoc w planowaniu i organizacji lub udzielanie wsparcia finansowego w ramach programów rolnośrodowiskowych w motywowaniu rolników do budowy niewielkich zbiorników wodnych (ang. „constructed wetlands”) na cele ochrony jakości wody na terenach rolniczych. Farmerzy uważają, że system wsparcia jest zbyt zbiurokratyzowany i dlatego liczba nowych zbiorników jest dużo mniejsza od spodziewanych. Indywidualne projekty podejmowane z inicjatywy rolników są dużo efektywniejsze w stosunku do oficjalnego wsparcia. Ogólnokrajowe plany skierowane głównie na obszary „hot spots” są przykładem jednej z barier ograniczających szerokie zastosowanie małych zbiorników do ochrony jakości wody. Mimo dość krytycznej oceny, oficjalny system wsparcia jest jednak niezbędny. Szersze zastosowanie niewielkich zbiorników wodnych do ograniczenia zagrożeń wody w wyniku dopływu zanieczyszczeń z obszarów użytkowanych rolniczo wymaga zwiększenia uprawnień władz lokalnych do typowania obszarów, na których celowa jest budowa tego typu urządzeń. Zadania związane z budową zbiorników do oczyszczania wody powinny być uwzględniane w zlewniowych planach gospodarowania wodą.