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Relative Effects of Land Use and Near-Stream Chemistry on Phosphorus in an Urban Stream

^a Hawaii Tokai International College, 2241 Kapiolani Blvd., Honolulu, HI 96826
^b Environmental Science and Resources, P.O. Box 751, Portland State Univ., Portland, OR 97207-0751

View larger version (39K): [in this window] [in a new window]   Fig. 1. (a) Map of the Johnson Creek watershed, Portland, OR, USA. Solid squares indicate sample sites within urban land use areas, while solid circles indicate sample sites in nonurban areas. (b) The shaded area indicates Troutdale Gravel aquifer (TG), while the nonshaded area indicates Unconsolidated Sedimentary aquifer (US) at surface level. The thick line indicates location of urban growth boundary (UGB); west of the UGB are urban land use areas, while east of the UGB are nonurban land use areas. RM = river miles from the mouth of the stream.

View larger version (22K): [in this window] [in a new window]   Fig. 2. Mean soil phosphorus content. Shown from urban (n = 8) and nonurban (n = 5) sites are: (a) mean water-soluble P content, (b) mean acid-soluble phosphorus content, (c) mean base-soluble P content, and (d) mean total P content. Dots indicate range of variation; whiskers indicate 5th and 95th percentiles; solid lines indicate median values; and dashed lines indicate means. Median values between urban and nonurban samples were significantly different in (a) water-soluble P contents and in (b) acid-soluble P contents for both the A and B horizons (p < 0.05).

View larger version (13K): [in this window] [in a new window]   Fig. 3. Mean soil pH, soil aluminum content, and soil iron content. Shown from urban (n = 8) and nonurban (n = 5) sites are: (a) mean soil pH, (b) mean soil Al content, and (c) mean soil Fe content. Dots indicate range of variation; whiskers indicate 5th and 95th percentiles; solid lines indicate median values; and dashed lines indicate means. Means between urban and nonurban samples were significantly different for soil pH in the A and B horizons (p < 0.01). Median values between urban and nonurban samples were significantly different (t test) for soil Al and Fe in the A and B horizons (p 0.001) (after Sonoda et al., 2002).

View larger version (18K): [in this window] [in a new window]   Fig. 4. Relationships between beneath-stream groundwater phosphorus concentrations vs. soil aluminum and soil iron contents at each site. Phosphorus concentration values are based on annual average (n = 12), whereas soil data are based on an average of 4 samples per site. Shown are (a) groundwater soluble reactive phosphorus (SRP) vs. Al in the B horizon, (b) groundwater total phosphorus (TP) vs. Al in the B horizon, (c) groundwater SRP vs. Fe in the A horizon, and (d) groundwater TP vs. Fe in the A horizon. Solid lines indicate significant (p < 0.05) linear regression slopes between near-stream groundwater phosphorus concentration and soil Al or soil Fe content.

View larger version (24K): [in this window] [in a new window]   Fig. 5. Mean stream water and near-stream groundwater phosphorus concentrations ± 1 standard deviation. Phosphorus concentration values are based on annual average (December 2000 through December 2001; n = 12). Shown are: (a) mean stream water soluble reactive phosphorus (SRP), (b) mean stream water total phosphorus (TP), (c) mean beneath-stream groundwater SRP, and (d) mean beneath-stream groundwater TP. Solid circles indicate urban sites, whereas open circles indicate nonurban sites. Error bars are standard error from the mean. Solid horizontal lines indicate mean concentrations of all urban sites, whereas dotted horizontal lines indicate mean concentrations of all nonurban sites.

View larger version (16K): [in this window] [in a new window]   Fig. 6. Seasonal average phosphorus flux at each sample site. Closed circles indicate wet season average value (n = 19 for each location), whereas open circles indicate dry season average values (n = 15 for each location). (a) Soluble reactive phosphorus (SRP) flux in µg s–1. (b) Total phosphorus (TP) flux in µg s–1. Error bars are ± 1 standard error (SE) from the mean.

View larger version (28K): [in this window] [in a new window]   Fig. 7. Mean stream vs. near-stream groundwater phosphorus concentrations. Phosphorus concentration values are based on annual average (December 2000 through December 2001; n = 12). Shown are: (a) urban soluble reactive phosphorus (SRP), (b) nonurban SRP, (c) urban total phosphorus (TP), and (d) nonurban TP. Error bars are ± 1 standard error (SE) from the mean. Solid lines indicate significant linear regression slopes (for 7b, adj. R2 = 0.975; for 7d, adj. R2 = 0.573) between stream water and near-stream groundwater phosphorus concentrations (after Sonoda et al., 2002).