Sediment and Nutrient Retention in Ponds on an Agricultural Stream: Evaluating Effectiveness for Diffuse Pollution Mitigation

Abstract

The creation of ponds and wetlands has the potential to alleviate stream water quality impairment in catchments affected by diffuse agricultural pollution. Understanding the hydrological and biogeochemical functioning of these features is important in determining their effectiveness at mitigating pollution. This study investigated sediment and nutrient retention in three connected (on-line) ponds on a lowland headwater stream by sampling inflowing and outflowing concentrations during base and storm flows. Sediment trapping devices were used to quantify sediment and phosphorus accumulations within ponds over approximately monthly periods. The organic matter content and particle size composition of accumulated sediment were also measured. The ponds retained dissolved nitrate, soluble reactive phosphorus and suspended solids during baseflows. During small to moderate storm events, some ponds were able to reduce peak concentrations and loads of suspended solids and phosphorus; however, during large magnitude events, resuspension of deposited sediment resulted in net loss. Ponds filtered out larger particles most effectively. Between August 2019 and March 2020, the ponds accumulated 0.306 t ha−1 sediment from the 30 ha contributing area. During this period, total sediment accumulations in ponds were estimated to equal 7.6% of the suspended flux leaving the 340 ha catchment downstream. This study demonstrates the complexity of pollutant retention dynamics in on-line ponds and highlights how their effectiveness can be influenced by the timing and magnitude of events.

Dredging impact on water quality in Bomuruella Reservoir in Nuwara Eliya, Sri Lanka

“…There was a significant decrease in BOD and phosphate levels before and after dredging in Lunawa Lagoon, which could be due to the removal of organic sediments with dredged materials (Perera and De Alwis 2011). According to Pettersson (1998) and Robotham et al, (2021), fine-grain sediment consists of high concentrations of soluble nitrogen and phosphorus. Phosphates levels could be increased as a result of excessive fertilization loaded in the reservoir that is discharged to the water body from the agricultural canals.…”

Nature‐based solutions enhance sediment and nutrient storage in an agricultural lowland catchment

“…P10_US_OLP had an exceptionally high rate compared to other online features because it is the most upstream feature in a series of three connected features. Robotham et al (2021) showed that P10_US_OLP was generally the most effective at trapping sediment. Therefore, where NBS interventions are placed in series, features that are located farthest upstream are likely to require more frequent maintenance.…”

“…The studied features were constructed between February 2018 and February 2019 and vary in their design and hydrology (Table 1). Further details on the Littlestock Brook NFM trial are given by Old et al (2019) and Robotham et al (2021).…”

“…Without appropriate management, there is a risk that online features may act as a source of sediment and pollutants (Barber & Quinn, 2012). However, evidence shows that overall, such features are still net sediment sinks despite their potential to act as temporary sources during large events (Robotham et al, 2021). Whilst more frequent desilting makes online features more expensive to maintain, they have potential for high nat- The design and configuration of online and offline features can play an important role in their ability to effectively intercept and store water and eroded matter.…”

Novel sediment source fingerprinting quantifying erosion-induced total nitrogen and total phosphorus outputs from an intensive agricultural catchment, North China

“…Consequently, the increasing soil erosion by intensified agricultural practices and associated N and P contaminants lead to environmental and water pollution (Robotham et al, 2021;Wang et al, 2021).…”