E. coli
Understanding the sources of E. coli
Faecal source tracking identifies the source of contamination by identifying the microorganisms that are specific to the gut of animals or humans.
In 2015 and 2016, Environment Southland and ESR undertook water quality and faecal source tracking analysis of samples collected across the Aparima, Matāura, Ōreti and Waiau catchments. Some sites had a single sample collected, while others had multiple samples (up to six) collected. Some sites were sampled under both base flow (i.e. dry) and high flow (i.e. post-rainfall) conditions, while others were sampled under one or the other.
Read the full report here>
Aparima catchments
A total of 27 sites were sampled in the Aparima catchments, although many were sampled on a single occasion and during dry weather. Ruminant animals (including sheep and cows) and wildfowl were important sources of faecal pollution, and multiple source markers were often detected in the same sample.
Wildfowl pollution was detected at 23 sites overall. Of the nine sites where multiple samples were collected, wildfowl markers were detected at six sites. Wildfowl pollution at these sites was ubiquitous, being present in virtually all samples collected, with similar prevalence regardless of whether samples were collected follow wet or dry conditions. Wildfowl was likely a dominant pollution source under base flow conditions.
Ruminant faecal pollution was detected at all 27 sites, although in highly varied amounts: under base flow, ruminants were a minor source at some sites (~1% of total faecal pollution), and dominant (50-100%) at others. Sheep markers were detected more frequently than cow markers at sites with repeated sampling. For samples collected following rainfall however, ruminants typically dominated the faecal input, with both sheep and cow markers being detected at similar rates.
Oreti catchments
Faecal source tracking analysis of samples from 13 sites in the Oreti catchments found that ruminant animals (including sheep and cows) and wildfowl were important sources of faecal pollution. Samples often contained multiple source markers at the same time.
Wildfowl pollution was detected at all 13 sites. Wildfowl markers were detected in 90% of the samples collected under base flow conditions, and 61% of samples collected following rainfall. Wildfowl are likely to be the dominant faecal source under dry conditions. Following rainfall however, ruminant animals were the dominant faecal source, with both sheep and cow markers being detected more frequently. Cow faecal markers were detected at all 13 sites, with sheep markers detected at 12 sites overall.
Although only a small set of samples were tested for the presence of dog faeces, markers were detected at Otepuni Creek at Nith Street, and Tussock Creek at Cooper Road.
Mataura catchments
Faecal source tracking analysis of samples from 15 sites in the Mataura catchments found that sheep, cows and wildfowl were important sources of faecal pollution. Samples often contained multiple source markers at the same time.
Wildfowl pollution was detected at 14 sites, and was detected with similar frequency regardless of whether samples were collected under wet or dry conditions. Birds were likely the dominant source of pollution under dry conditions. Following rainfall, ruminant animals became the primary source of pollution. Overall, cow markers were specifically detected at 13 sites and sheep markers at 12 sites, and both were detected more frequently following rainfall, suggesting they both contribute to the increased ruminant loading during high flow conditions.
Waiau catchments
Faecal source tracking analysis of samples collected from five sites in the Waiau catchments indicated that ruminant animals (including both cows and sheep) and wildfowl were important sources of pollution. Ruminant markers were detected at all sites, and wildfowl at four sites.
Although only a limited number of samples were collected, the ruminant contribution tended to be greater at sites further down the catchment. Whilst both sheep and wildfowl markers were detected under both wet and dry conditions, wildfowl was likely to be a main source of pollution under base flow conditions. Following rainfall, ruminant pollution became dominant. More frequent detection of both sheep and cow markers (the latter being detected only after rainfall) suggests they are major sources of pollution under high flow conditions.
Human faecal pollution in the Southland region
Human faecal contamination was detected at five sites across the Oreti catchments: Bog Burn downstream of Hundred Line Road; Makarewa River at Lora Gorge Road; Otepuni Creek at Nith Street; Waihopai River upstream of Queen’s Drive; and Waikiwi Stream at North Road. In particular, human markers were repeatedly detected in Otepuni Creek (all four samples collected), the Waihopai River (3 of 6 samples) and Waikiwi Stream (3 of 6 samples). The repeated detection of human markers at these sites is perhaps not surprising, given the urban land uses immediately upstream of sampling locations.
Human faecal contamination was detected at six sites in the Aparima catchments: the Otautau Stream at both Otautau-Tuatapere Road and at Waikouro; the Wairio Stream at both Birchwood-Wairio Road and upstream of the confluence with the Otautau Stream; the Opouriki Stream at Tweedie Road; and and the Waimatuku Stream at the Lorneville-Riverton Highway.
There was one instance of human faecal pollution in the Mataura catchments, at Oteramika Stream at Seaward Downs. This was detected under base flow conditions.
No instances of human pollution were detected in the Waiau catchments.
