Wetlands

A 2.5 km stretch of a sandur (glacial outwash plain) neighbouring a wetland in South-east Iceland was monitored from 1 September 2015 to 2 September 2016. Improved understanding of the hydrological regime at this sandur-wetland boundary is warranted as local farmers are losing ground to the frequent flooding of their wet meadows despite the existence of elevated berms. A series of water wells were installed across a sandur-wetland boundary, to monitor water table fluctuations, determine flooding extent and assess groundwater inflow. Flooding occurred rapidly in the sandur during 19 weather events, which included modest and heavy rainfall, and glacial outburst floods (jökulhlaups). Water levels on the South-western edge of the wetland responded in sync with the sandur during flooding, indicating a connectivity via groundwater exchange across the coarse, non-vegetated berm. We estimated that between 6 June and 31 August, 11,275 m3 of groundwater flowed from the sandur to this part of the wetland. This contrasted with the South-eastern edge of the wetland, which had an older, vegetated berm. Here, only 7446 m3 of groundwater flowed from the sandur to the wetland. Overall, these modest water inputs accounted for 76% of seasonal evaporation loss from the wetland (191 mm).

Wetlands in central North Dakota were revisited after 50 years to assess changes following extreme drought and a prolonged wet period. We compared data collected during 1961–1966 to current (2013–2014) wetland conditions. We revisited 80 wetlands in 2013 and 2014 across three study areas and measured wetland area, ponded-water depth, and specific conductance. Wetlands at the three study areas responded to prolonged wet conditions in one of three ways. Wetlands at Crystal Springs became larger, and had deeper ponds of lower specific conductance in 2013–14 compared to the 1960s. Wetlands at Cottonwood were larger with deeper ponds of slightly higher specific conductance in 2013–2014. Wetlands at Mt. Moriah had only subtle changes in size, pond depth, and specific conductance between periods. Prolonged wet conditions led to merging of most wetlands (defined as the outer edge of wet-meadow vegetation) at Crystal Springs and a few wetlands at Cottonwood. Low topographic relief at Crystal Springs and Cottonwood contributed to storage of excess water in wetlands with associated responses to prolonged wet conditions. In contrast, higher topographic relief and natural outlets into two intermittent streams at Mt. Moriah resulted in wetlands being less impacted by prolonged wet conditions.

Invasive plants are a growing concern worldwide for conservation of native habitats. In endangered wet meadow habitat in the Upper Midwestern United States, reed canary grass (Phalaris arundinacea) is a recognized problem and its prevalence is more widespread than the better-known invasive wetland plant purple loosestrife (Lythrum salicaria). Although resource managers are concerned about the effect of reed canary grass on birds, this is the first study to report how common wet meadow birds use habitat in relation to reed canary grass cover and dominance. We examined three response variables: territory placement, size of territories, and numbers of territories per plot in relation to cover of reed canary grass. Territory locations for Sedge Wren (Cistothorus platensis) and Song Sparrow (Melospiza melodid) were positively associated with reed canary grass cover, while those for Common Yellowthroat (Geothlypis trichas) were not. Only Swamp Sparrow (M. georgiana) territory locations were negatively associated with reed canary grass cover and dominance (which indicated a tendency to place territories where there was no reed canary grass or where many plant species occurred with reed canary grass). Swamp Sparrow territories were positively associated with vegetation height density and litter depth. Common Yellowthroat territories were positively associated with vegetation height density and shrub cover. Song Sparrow territories were negatively associated with litter depth. Reed canary grass cover within territories was not associated with territory size for any of these four bird species. Territory density per plot was not associated with average reed canary grass cover of plots for all four species. Sedge Wrens and Song Sparrows may not respond negatively to reed canary grass because this grass is native to wet meadows of North America, and in the study area it merely replaces other tall lush plants. Avoidance of reed canary grass by Swamp Sparrows may be mediated through their preference for wet areas where reed canary grass typically does not dominate.

Approximately 95 % of nearly 4 million acres of wetlands located in Iowa’s portion of the Prairie Pothole Region (Des Moines Landform Region) are currently drained and farmed for row-crop agriculture. Many of these wetland basins are too wet to produce consistent crop yields and too dry to function as ecologically intact wetlands. Little information currently exists that documents what, if any value, drained wetlands may have in terms of water quality, wildlife usage and/or habitat, and key hydrological aspects. A four-year comprehensive study of drained wetlands was carried out from 2011 to 2014 to document the ecological health of these ecosystems, including the measurement of pesticide levels (including neonicotinoids in 2014). Pesticides were found in more than 60 % of samples and the most frequently detected were chloroacetanilide and triazine pesticides and associated degradate products. At times, concentrations of pesticides exceeded aquatic life benchmarks. The neonicotinoid pesticides were also detected frequently with Clothianidin being the most frequently detected (98 % of samples), followed by Thiamethoxam (54 %), and Imidacloprid (48 %). Pesticide concentration levels were then compared to high quality reference wetlands in the same region. Information from this study advances the knowledge of drained wetlands for both conservation and land-use policy related decisions.

Tidal marshes play an important functional role in removing nitrogen (N) pollution before delivery to coastal and ocean systems; however, little is known about their removal capacity as N2O gas emissions from different plant species. To evaluate the effects of N inputs on N2O emissions from tidal marshes, we measured N2O fluxes from native (Cyperus malaccensis) and invaded (Spartina alterniflora) tidal marshes in the Min River estuary, and fertilized with exogenous N at the rates of 0, 21 and 42 g N m−2 yr.−1, respectively. S. alterniflora invasion did not significantly influence N2O emissions from the C. malaccensis marsh under natural conditions, but under N addition conditions, the invasion of S. alterniflora decreased N2O emissions, primarily owing to its stronger N uptake capacity. Exogenous N had significant positive effects on N2O fluxes in both native and invaded tidal marshes. Moreover, significant temporal variability of N2O fluxes was observed after N was gradually added to the native and invaded marshes. Within 3 h of N addition, N2O fluxes were significantly higher in plots receiving N additions relative to controls. After 8 days, few significant differences were found between treatments. Moreover, electrical conductivity, pH and oxidation-reduction potential at different soil depths were not significantly affected by N addition. Considering N addition showed extremely high positive effects on N2O fluxes at the hours scale, the overall increase of N2O emissions from wetlands in response to N addition may be significantly underestimated. To better assess the global climatic role of salt marshes that have been affected by N addition, the short-term temporal variability of N2O emissions should receive greater attention.

We monitored vegetation changes in an alpine mire after stopping an experiment of nutrient addition, during which the mire experienced a heat wave. We aimed at assessing the capacity of mire vegetation to recover towards the original state. Nitrogen and phosphorus were added during the growing seasons of 2002–2009. We recorded periodically the cover of all vascular plant species and moss species from 2002 to 2012, i.e., 9 years after the heat wave and 3 years after discontinuing fertilization. The principal effect of the 2003 heat wave consisted in a rapid increase in cover of vascular plants and a parallel decrease in cover of mosses. These trends slowed down after 6 years and almost totally halted 9 years after the heat wave. The heat wave was the main driver of vegetation changes but the vegetation also responded to fertilization. Species within plant functional types (PFTs) showed differing responses to the heat wave and/or fertilization. The mire vegetation showed poor capacity to recover towards the initial conditions. Changes in vegetation composition were determined by individualistic responses of species to varying ecological factors. Grouping plant species into PFTs may conceal important differences in the responses of mire vegetation to environmental changes.

Intermittent loading is often used in constructed wetlands (CW) to improve water purification capacity, however, little is known of its impact on greenhouse gas (GHG) emissions.. We studied GHG fluxes in three CWs for municipal wastewater treatment in Estonia: the hybrid CW in Kõo had an intermittently loaded (8–10 pulses a day) vertical subsurface flow (VSSF) filter and a horizontal subsurface flow (HSSF) filter with stable water level (10 cm below the surface), the HSSF filter in Kodijärve with higher (42 cm) but more fluctuating water level (from 5 to 75 cm) in inflow and lower (52 cm) but stable water level (30–70 cm) in outflow, and the HSSF filter in Paistu with fluctuating water table (0–70 cm). Intermittent loading enhanced N2O emissions from the VSSF filter in Kõo and the inflow parts of the HSSF in Kodijärve. Due to higher organic loading rates in the inflow part of the HSSF in Kodijärve and in the VSSF filter in Kõo, the fluctuating water table/intermittent loading did not influence the CO2 and CH4 fluxes. The lower water depths in Paistu resulted in higher CO2 and N2O, and lower CH4 emissions relative to other systems.

We examined the response of aquatic macroin vertebrates to three marsh management strategies. The three management practices compared were conventional full pool management, full pool management with carp(Cyprinus carpio) control, and controur furrowing (also with carp control). Significant differences in standing crops (both numbers and biomass) of invertebrates were observed among the three management strategies. The contour furrowed area had the highest standing crops of water column invertebrates, followed by the carp-controlled full pool area, while the conventionally managed area had the lowest standing crops. In the benthos, the two full pool areas (with and without carp) had higher standing crops than the contour furrowed area. Significant differences were noted in seasonal abundance, with all management practices having lowest densities of invertebrates in April and May. Implications for management include indications of the negative impacts of carp and winter drawdowns on invertebrates in managed marshes.