Spatio‐temporal patterns of nutrient concentrations and export in a north‐eastern European lowland catchment

Abstract

Abstract:In 2002-2004 we undertook six sampling campaigns during representative hydrological stages in a 901 km 2 Estonian lowland catchment to quantify the spatial and seasonal variability of in-stream dissolved inorganic nitrogen (DIN) and dissolved reactive phosphorus (DRP) concentrations and to identify the influence of land cover and landscape structure. Using a synoptic approach we mapped concentrations in all stream orders. Using linear regression, the relations between the share of agricultural land and log-transformed in-stream concentrations were explored. Both the share of agricultural land in the entire 'area of influence' upstream from a sampling location, as well as the share in a 150-m buffer around the stream were used as linear regression input variables. Log-transformed DIN and DRP concentration variability was highest for lower order streams, while it averaged out in higher order streams during all seasons. Between-season variation in export can mainly be attributed to discharge variation. In extremely dry periods, there are no significant relations between land cover/structure and in-stream ln(DIN) concentrations and only weak relations for ln(DRP) concentrations. In other seasons, the share of agricultural land in the upstream area can explain concentrations in higher order streams better than in lower order streams. The prediction of ln(DIN) concentrations in lower order streams can be improved by using the share of agricultural land in a 150-m buffer as an input variable. This indicates that hydrological connectivity must be taken into account for lower order streams, while land cover shares are enough to explain concentrations for higher order streams.

Seasonally Driven Variation in Spatial Relationships Between Agricultural Land Use and In‐stream Nutrient Concentrations

“…Stronger linkages between land use in corridor areas and in‐stream nutrient conditions, as opposed to the entire catchment, have been documented in other studies (e.g. Osborne and Wiley, ; Mourad and van der Perk, ), but not all (e.g. Omernik, ; Hunsaker and Levine, ).…”

“…The relationship between in‐stream nutrient concentrations and land use has been demonstrated to be strongly and positively linked to stream‐flow conditions (e.g. Petry et al ., ; Buck et al ., ; Mourad and van der Perk, ; Chun et al ., ). Given that stream flow is strongly associated with precipitation conditions and associated runoff in the catchment areas, wetting or drying conditions within the catchment should result in the expansion or contraction of the areas of land associated with in‐stream nutrient conditions.…”

Groundwater impacts on surface water quality and nutrient loads in lowland polder catchments: monitoring the greater Amsterdam area

“…For example, Van Beek et al (2007) found that nutrient-rich peat layers will remain a potential source of nutrients in surface water in many peat polders in the western part of the Netherlands. Mourad and van der Perk (2009) found that the spatial patterns of nitrate and phosphate concentrations in the Ahja River catchment in Estonia were related to spatial differences in urban and agricultural land use proportions. Vermaat et al (2010) studied 13 peat polders in the Netherlands and reported that agricultural land use largely determined the variability in nutrient concentrations and loads.…”