Refill disused borrow pits
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
'Aggregates’ is the collective term for sand, gravel and crushed rock. They are used as raw materials for the construction industry as well as for beach replenishment schemes (De Groot 1996). Extraction leads to physical impacts and disruption of the seabed, including the formation of borrow pits, also known as dredged holes (Reine et al. 2013). Borrow pits tend to be very different from the surrounding natural seabed, being much deeper, isolated, and of different sediment type. The natural seabed ecology could be restored by refilling the disused borrow pits following cessation of extraction (Reine et al. 2013). This can potentially help the recolonization and natural recovery of the invertebrate community.
Evidence for interventions related to aggregate extraction is summarised under “Threat: Energy production and mining – Mining and quarrying”.
De Groot S.J. (1996) The physical impact of marine aggregate extraction in the North Sea. ICES Journal of Marine Science, 53, 1051–1053.
Reine K., Clarke D., Ray G. & Dickerson C. (2013) Fishery resource utilization of a restored estuarine borrow pit: A beneficial use of dredged material case study. Marine Pollution Bulletin, 73, 115–128.
Supporting evidence from individual studies
A before-and-after, site comparison study in 2004–2007 of two soft seabed sites in Barnegat Bay estuary, New Jersey, USA (Reine et al. 2013) found that partially refilling a disused borrow pit led to increased invertebrate species richness, abundance and diversity after 2–3 years, but these remained lower than at a nearby natural site. Refilling the pit increased average species richness (before: 1–13; after: 14–24 taxa/sample), abundance (before: 0–144; after: 151–495 individuals/sample) and diversity (presented as diversity indices) but these remained lower than at the natural site (species: 40; abundance: 1,370). Abundance at the natural site had increased over the same time (before: 435; after: 1,370) and species richness remained stable (before: 40; after: 40). In 2004, a borrow pit was partially filled with dredged sand, reducing its depth from 11.5 m to 6 m and increasing relief complexity-. Once in 2006 and twice in 2007, eighteen sediment samples were collected at the restored pit and six at a nearby natural site using a grab (0.044 cm2, 6 cm depth). Invertebrates (>0.5 mm) were identified and counted. Data post-restoration (2006 and 2007) were pooled. Data prior to restoration were obtained from Versar (1999).
Versar (1999). Biological sampling for dredged holes in Barnegat Bay, Ocean County, NJ. Data Report prepared for the US Army Corps of Engineers, Philadelphia District, Philadelphia, PA.Study and other actions tested