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Causal connections between water quality and land use in a rural tropical island watershed: rural tropical island watershed analysis.

Ragosta G, Evensen C, Atwill ER, Walker M, Ticktin T, Asquith A, Tate KW - Ecohealth (2010)

Bottom Line: Each 1% decrease in riparian canopy cover was associated with a 4.6 most probable number (MPN)/100 ml increase of the geometric mean of Enterococcus in stream water (P < 0.05).Each unit decrease in salinity (ppt) was associated with an increase of Enterococcus by 68.2 MPN/100 ml in-stream water geometric mean concentrations (P < 0.05).Reducing riparian canopy cover is associated with Enterococcus increases in stream water, suggesting that decreasing riparian vegetation density could increase fecal bacteria surface runoff.

View Article: PubMed Central - PubMed

Affiliation: Surfing Medicine International 501(c)(3), 5-5785A Kuhio Highway, Hanalei, HI 96714, USA. surfingmedicine@gmail.com

ABSTRACT
We examined associations between riparian canopy cover, presence or absence of cattle, rainfall, solar radiation, month of year, dissolved oxygen, turbidity, salinity, and Enterococcus concentrations in riparian surface soils with Enterococcus geometric mean in-stream water concentrations at Waipā watershed on the north side of the Hawaiian island Kaua'i. Each 1% decrease in riparian canopy cover was associated with a 4.6 most probable number (MPN)/100 ml increase of the geometric mean of Enterococcus in stream water (P < 0.05). Each unit decrease in salinity (ppt) was associated with an increase of Enterococcus by 68.2 MPN/100 ml in-stream water geometric mean concentrations (P < 0.05). Month of year was also associated with increases in stream water Enterococcus geometric mean concentrations (P < 0.05). Reducing riparian canopy cover is associated with Enterococcus increases in stream water, suggesting that decreasing riparian vegetation density could increase fecal bacteria surface runoff.

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Plot locations and water quality monitoring sites.
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Fig2: Plot locations and water quality monitoring sites.

Mentions: Our monitoring sites were in Waipā watershed on the rural Hawaiian island Kaua’i (Fig. 1, 2). The watershed encompasses about 650 hectares from sea level to Mamalahoa Summit at 1141 m above sea level. Middle to upper elevation Waipā riparian zones, unmanaged and uninhabited by people, provide an environment where nonnative invasive plants such as Psidium cattleianum Sabine and Psidium guajava Linnaeus have spread rapidly, in part because they are food sources for horses, pigs, rats, and birds, which eat the fruits and disperse seeds from these plant species. Lower elevation Waipā contains streamflow diversions and water transport via ditches used to irrigate the vegetable taro (Colocasia esculenta [Linnaeus] Schott). The watershed near sea level also has several rural residences, a two-lane paved road, a community center, small agricultural plots, about 50 rodeo cattle that graze an approximately 2-hectare paddocked pasture (< 100 m from sites 1 and 2), and a few cattle and horses that stay outside the paddock (< 100 m from site 3). Surface soil in Waipā’s riparian zones varies in texture from extremely compacted loamy sand soils along the cattle pasture irrigation diversion ditch, near site 2 around sea level, to rocks and boulders mixed with silty clay loam soils in the upper elevations of the watershed. Cattle grazed along Kapalikea tributary until the late 1960’s when land managers confined remaining cattle around sites 1, 2, and 3. During the study period, most of the approximately 50 cattle congregated and grazed daily within 100 m of sites 1 and 2, with a lesser density of cattle grazing < 100 m from site 3 (outside the approximately 2-hectare paddock surrounding sites 1 and 2). Roads and other structures make it more difficult for cattle to cross from site 2 (located at the end of a cattle pasture irrigation diversion ditch) to site 1 (located at Waipā Stream mouth). Residents may also contribute Enterococci from leaching sewage to site 1 at sea level, which is the only site below residences at Waipā. Cattle were never present at sites 4, 5, 6, or 7 due to confinement and active management, and rugged topography too difficult for cattle to access. The irrigation diversion ditch that runs along the cattle pasture near sea level drains surface runoff to site 2, which exits via a culvert into Waipā Stream mouth at site 1, flowing directly into Hanalei Bay.Figure 2


Causal connections between water quality and land use in a rural tropical island watershed: rural tropical island watershed analysis.

Ragosta G, Evensen C, Atwill ER, Walker M, Ticktin T, Asquith A, Tate KW - Ecohealth (2010)

Plot locations and water quality monitoring sites.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2914289&req=5

Fig2: Plot locations and water quality monitoring sites.
Mentions: Our monitoring sites were in Waipā watershed on the rural Hawaiian island Kaua’i (Fig. 1, 2). The watershed encompasses about 650 hectares from sea level to Mamalahoa Summit at 1141 m above sea level. Middle to upper elevation Waipā riparian zones, unmanaged and uninhabited by people, provide an environment where nonnative invasive plants such as Psidium cattleianum Sabine and Psidium guajava Linnaeus have spread rapidly, in part because they are food sources for horses, pigs, rats, and birds, which eat the fruits and disperse seeds from these plant species. Lower elevation Waipā contains streamflow diversions and water transport via ditches used to irrigate the vegetable taro (Colocasia esculenta [Linnaeus] Schott). The watershed near sea level also has several rural residences, a two-lane paved road, a community center, small agricultural plots, about 50 rodeo cattle that graze an approximately 2-hectare paddocked pasture (< 100 m from sites 1 and 2), and a few cattle and horses that stay outside the paddock (< 100 m from site 3). Surface soil in Waipā’s riparian zones varies in texture from extremely compacted loamy sand soils along the cattle pasture irrigation diversion ditch, near site 2 around sea level, to rocks and boulders mixed with silty clay loam soils in the upper elevations of the watershed. Cattle grazed along Kapalikea tributary until the late 1960’s when land managers confined remaining cattle around sites 1, 2, and 3. During the study period, most of the approximately 50 cattle congregated and grazed daily within 100 m of sites 1 and 2, with a lesser density of cattle grazing < 100 m from site 3 (outside the approximately 2-hectare paddock surrounding sites 1 and 2). Roads and other structures make it more difficult for cattle to cross from site 2 (located at the end of a cattle pasture irrigation diversion ditch) to site 1 (located at Waipā Stream mouth). Residents may also contribute Enterococci from leaching sewage to site 1 at sea level, which is the only site below residences at Waipā. Cattle were never present at sites 4, 5, 6, or 7 due to confinement and active management, and rugged topography too difficult for cattle to access. The irrigation diversion ditch that runs along the cattle pasture near sea level drains surface runoff to site 2, which exits via a culvert into Waipā Stream mouth at site 1, flowing directly into Hanalei Bay.Figure 2

Bottom Line: Each 1% decrease in riparian canopy cover was associated with a 4.6 most probable number (MPN)/100 ml increase of the geometric mean of Enterococcus in stream water (P < 0.05).Each unit decrease in salinity (ppt) was associated with an increase of Enterococcus by 68.2 MPN/100 ml in-stream water geometric mean concentrations (P < 0.05).Reducing riparian canopy cover is associated with Enterococcus increases in stream water, suggesting that decreasing riparian vegetation density could increase fecal bacteria surface runoff.

View Article: PubMed Central - PubMed

Affiliation: Surfing Medicine International 501(c)(3), 5-5785A Kuhio Highway, Hanalei, HI 96714, USA. surfingmedicine@gmail.com

ABSTRACT
We examined associations between riparian canopy cover, presence or absence of cattle, rainfall, solar radiation, month of year, dissolved oxygen, turbidity, salinity, and Enterococcus concentrations in riparian surface soils with Enterococcus geometric mean in-stream water concentrations at Waipā watershed on the north side of the Hawaiian island Kaua'i. Each 1% decrease in riparian canopy cover was associated with a 4.6 most probable number (MPN)/100 ml increase of the geometric mean of Enterococcus in stream water (P < 0.05). Each unit decrease in salinity (ppt) was associated with an increase of Enterococcus by 68.2 MPN/100 ml in-stream water geometric mean concentrations (P < 0.05). Month of year was also associated with increases in stream water Enterococcus geometric mean concentrations (P < 0.05). Reducing riparian canopy cover is associated with Enterococcus increases in stream water, suggesting that decreasing riparian vegetation density could increase fecal bacteria surface runoff.

Show MeSH
Related in: MedlinePlus