Factors affecting retention of nutrients and organic matter in stormwater ponds

Abstract

Stormwater ponds are a common way to handle urban runoff. Different pond designs have been tested for decades to retain as much water as possible. Lately also, retention of nutrients and organic matter has become increasingly important, to reduce the eutrophication of downstream aquatic systems and thereby, e.g. fulfil the European Water Framework Directive. We have examined the load of particulate and dissolved fractions of organic matter, phosphorus, nitrogen and iron in 66 Danish ponds to determine the importance of catchment type (66 ponds) and the retention efficiency of the ponds (39 ponds) dependent on their type, age, size and design. The results showed that discharge from nutrient enriched and industrial areas is the most polluted while urban and developing areas are the least polluted. Wet ponds combined with vegetated sand filters have higher retentions of the particulate fractions (40-80%) compared with traditional wet ponds (10-20%). Generally, optimized retention requires a ratio between pond volume and impermeable catchment area of >250 m 3 red.ha (reduced or impermeable hectare). Young ponds have higher retention than older ones, especially regarding the particulate fractions of organic matter, phosphorus and nitrogen. Here, 40-50% is retained in ponds <5 years, 0-30% in 5-10-year-old ponds and almost nothing in ponds >10 years. For the dissolved fractions, the trend is the same, but with lower retentions. Therefore, management and maintenance should be considered for all ponds, to avoid problems of internal loading, filling and resuspension.

Ecological and Conservation Value of Small Standing-Water Ecosystems: A Systematic Review of Current Knowledge and Future Challenges

“…The remaining papers deal with the use of SWEs as biogeochemical reactors, able to ensure the achievement of good ecological status (as imposed by WFD) of related/connected larger water ecosystems (included in the WFD) at the basin scale, both in urban (as stormwater ponds) [47][48][49] and rural contexts [50][51][52][53]. The potential role of SWEs in controlling N and P retention was extensively explored, especially in Northern Europe (Denmark, Sweden, Norway), although more data is needed to better evaluate the effects of hydrologic pulsing on wetland metabolism and performance in the mid to long-term [50].…”

Mobility and Bioavailability of Sediment Phosphorus in Urban Stormwater Ponds

“…These small ponds remove nutrients by way of particle sedimentation, physical absorption, and uptake by resident biota, all of which could improve water quality downstream (Comings et al, 2000). While promoted as a possible nutrient sink (Brunberg & Boström, 1992;Maavara et al, 2015), stormwater ponds have been found to have highly variable (10-90%) and generally quite low (average~30-40%) retention efficiencies of P (Gold et al, 2017a(Gold et al, , 2017bSonderup et al, 2016). Variable and generally low retention efficiency of P in urban stormwater ponds may be partly explained by internal pond P biogeochemistry.…”

Urban Stormwater Characterization, Control, and Treatment

“…interestingly Sønderup et al (2016) found that when comparing P, N, and Fe removal efficiency of stormwater ponds, the ponds which were greater than 10 years old demonstrated no retention capabilities for particulate or dissolved constituents. This suggests that regular maintenance of ponds is critical and that decreases in performance should be considered when modeling future behavior.…”