Preprints of Extended Abstracts Vol. 41 No. 1

ENVIRONMENTAL TRENDS (Cosponsored with ACS Committee on Environmental Improvement

Organized by

T.L. Wade

Symposia Papers Presented Before the Division of Environmental Chemistry American Chemical Society San Diego, CA April 1-5, 2001

TRACE ELEMENTS IN THE AQUATIC ENVIRONMENT OF : EFFECTS OF URBANIZATION

Eric Heinen De Carlo1, Vincent L. Beltran1, Michael S. Tomlinson1, Khalil J. Spencer2 and Julia E. Hubert1 1Department of Oceanography, SOEST, University of Hawaii, 1000 Pope Road, , HI 96822 Fax: 808-956-7112, [email protected] 2Department of Geology and Geophysics, SOEST, University of Hawaii

In small subtropical island watersheds, material inputs to the ocean are dominated by freshwater pulses associated with intense but often abrupt orographic rainstorms. The rugged topography and high rainfall intensity typical of the main Hawaiian Islands results in rapidly changing hydrographic conditions that present an opportunity to study the spatial and temporal evolution of material as it travels through the watershed to the ocean. Because the island of , and Honolulu in particular, have been extensively urbanized during the second half of the 20th century, transport of suspended particulate matter (SPM) during storms represents an important vehicle for the mobilization of anthropogenic material deposited throughout the watersheds during the past half century.

Rainstorms generated by orographic uplift of warm and moist tradewinds often occur at night, when a rapid response and deployment of manual sampling equipment is difficult at best. Additionally, because the response of streams to storms in Oahu watersheds is rapid (e.g., Fig 2), automated sampling is imperative to capture samples from the representative limbs of rapidly changing hydrographs. We have established a network of automatic sampling and water quality monitoring stations in streams of high-relief watersheds on Oahu, Hawaii to evaluate the variability in material transported to estuaries and the coastal ocean during low flow and storm conditions Land use throughout the small (46.3 km2) Ala Wai Canal watershed, shown in Figure 1, is

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approximately 55% urban and 45% forested and conservation. A small portion of the latter also includes agricultural activities. More than 200,000 people call the watershed home, and over 250,000 vehicle trips are undertaken through it daily.

The goals of this study are to determine spatial and temporal trends in water quality in the watershed, to quantify storm-driven material fluxes to the ocean and elucidate natural and anthropogenic trace element contributions therein.

The trace element composition of water (Fig. 3) and SPM varies (spatially) downstream, largely reflecting anthropogenic inputs in urbanized areas, particularly where stream channels have been extensively modified (e.g., De Carlo and Spencer, 1997). Concentrations of trace elements in the dissolved and particulate phases, as well as the isotopic composition of Pb exhibit spatial and temporal variations during storms that attest to the variability of inputs of source materials. Although the bulk of the SPM carried through the watershed originates from the relatively pristine mountainous regions of the watershed, and is characterized by near background trace element concentrations, rapidly changing hydrographic conditions erode watershed soils and mobilize street dirt containing “averaged” anthropogenic metal signatures. Anthropogenic inputs of As, Cd, Pb, and to a lesser extent, Zn and Cu, to aqueous and particulate phases are readily identified, are most evident during “first flush” samples and strongly overprint the natural signal for these elements (Figs. 4 and 5).

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Figure 1. Shaded relief map of Ala Wai Canal Watershed, showing sampling and monitoring stations. WK is above urbanization, KW is located near the University of Hawaii just below large storm drain inputs to Manoa Stream, KHS is in the tidally influenced lowest portion of the watershed immediately upstream of the Ala Wai Canal estuary.

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Figure 2. Hydrograph for Manoa Stream at Stations WK and KHS during the rainstorm of the night of 1- 2 December 1999.

Figure 3. Concentrations of heavy metals in water from Manoa Stream and the Ala Wai Canal estuary collected during low-flow conditions. Note the increasing concentrations of Cu, Pb and Zn as a function of distance from the watershed divide. Concentrations of these elements decrease in the estuary owing to dilution by seawater. Elevated concentrations of Zn and Cu at Station YC are attributed to boat bottom paints and sacrificial anodes used in the harbor.

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Concentrations of Cu, Pb (e.g., Fig. 4) and Zn in SPM during storms display trends that are consistent with a large anthropogenic input of these elements in the urbanized portions of the watershed. Concentrations of elements displaying strong first flush signatures decrease as a function of time during storms, although in many cases they do not return to background levels expected in the absence of anthropogenic inputs. A small “first flush” signal for Cd, Zn, and Pb recurs in nearly all storms sampled at the upper watershed (WK) station, consistent with deposition of a small wind-borne anthropogenic aerosol component in conservation lands. Lead isotopic ratios determined in water and SPM samples collected throughout the watershed and coastal ocean as well as in growth bands of Porites lobata coral colonies indicate that the “upper watershed” Pb includes a small but persistent contribution from long-range transported aerosols from Asia. Background concentrations of Cu, Zn, Ni, and Cr observed in Hawaii are much higher than typically observed in continental settings, therefore substantial natural particulate loads of these elements are delivered to the coastal ocean annually.

Anthropogenic inputs of As are inferred to be derived mostly from agricultural activity in the upper watershed. High concentrations of As associated with SPM occur in “first flush” samples (Fig. 5) collected at the upper watershed station (WK, Fig. 1) during rising hydrographs.

WK TSS, 10/19/99 Storm KW TSS, 10/19/99 Storm KHS TSS, 10/19/99 Storm

35 40 1400 75 700 180 160 30 600 35 1200 65 140 25 1000 500 30 55 120 20 800 400 100 25 45 15 600 300 80 Flow (cfs) Flow (cfs) 20 35 Flow (cfs) 60 10 400 200 40 25 Pb Concentration (ppm) 5 15 200 Pb Concentration (ppm) 100 Pb Concentration (ppm) 20 0 10 0 15 0 0 15:36 16:48 18:00 13:12 15:36 18:00 13:12 15:36 18:00 Time (HST) Time (HST) Time (HST)

Figure 4. Temporal variations in the concentration of Pb in suspended particulate matter collected from three stations during the rainstorm of 10/19/1999

Initial solid phase As concentrations of over 100 µg/g decrease to 20-30 µg/g as eroded unpolluted soils begins to dilute the anthropogenic “first flush”signal. As concentrations in SPM at the lower watershed stations nearly double late during storms, consistent with a delayed downstream transport of anthropogenic As derived from the upper watershed.

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WK TSS, 10/19/99 Storm KW TSS, 10/19/99 Storm KHS TSS, 10/19/99 Storm

110 40 45 75 40 180 160 100 35 65 35 40 140 90 30 55 30 120 80 35 100 25 25 45 80 70 30 Flow (cfs)

Flow (cfs) Flow (cfs) 20 60 20 35 60 40 15 25 As Concentration (ppm) 15 25 As Concentration (ppm) 50 As Concentration (ppm) 20 10 0 40 10 20 15 13:12 15:36 18:00 15:36 16:48 18:00 13:12 15:36 18:00 Time (HST) Time (HST) Time (HST)

Figure 5. Temporal variations in the concentration of As in suspended particulate matter collected during the rainstorm of 10/19/1999

Long term time series data for DO, pH, temperature, conductivity, and turbidity will be discussed in terms of how stream modifications impact water quality. We will also review historical trends of heavy metal pollution in urban Honolulu as recorded from estuarine sediment cores.

Reference De Carlo, E.H. and Spencer, K.J., Retrospective analysis of anthropogenic inputs of lead and other metals to the Ala Wai Canal, Oahu, Hawaii. Applied Organometallic Chemistry, (1997) 11(4):415-437.

Acknowledgment This paper was funded in part by a grant from the National Oceanic and Adminsitration, project REL15, which is sponsored by the University of Hawaii Sea Grant College Program, SOEST, under Institutional Grant No. NA86RG0041 from the NOAA Office of Sea Grant, Department of Commerce. The views expressed herein are those of the authors and do not necessarirly reflect the views of NOAA or any of its subagencies. UNIHISEAGRANTCP0002. Additional funding from the USEPA, the USGS/Water Resource Research Institute, and the State of Hawaii, Department of Land and Natural Resources is gratefully acknowledged.

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