Kaneohe and Waimanalo streams on the windward side of the island of Oahu in the Hawaiian Islands have been hardened to prevent flooding. The hardening process has involved elimination of the natural riparian habitat and replacement of the natural stream channel with a concrete-lined conduit having vertical walls and a broad, flat bottom. The shallow depth of the water column and the absence of shade have resulted in temperatures that average as much as 4-5oC above ambient and rise as high as 32oC during daylight hours. Unlike most low-order streams, the hardened sections of both streams are autotrophic, as evidenced by elevated pH values and O2 concentrations as high as 150% of saturation. Several allochthonous inputs, one from a storm sewer and the other from a natural spring, introduced water with anomalously low O2 concentrations and very high nitrate concentrations. The absence of sediments in the hardened sections of the streams precludes natural sedimentary microbial processes, including denitrification. Nitrate concentrations in a section of Waimanalo Stream with a natural streambed drop dramatically from values in excess of 400 ?M to concentrations less than 10 ?M at the head of the estuary. Although some of this decline is due to dilution with seawater, the concentration of nitrate at the head of the estuary is only 10% of the value that could be explained by dilution effects. Biological processes associated with a natural streambed thus appear very important to the functionality of the streams and in particular to their ability to process allochthonous nutrient inputs in a way that minimizes impacts on the nearshore environment. Prevention of flooding can be accomplished by mechanisms that do not involve elimination of riparian buffer zones and destruction of channel habitat. To maintain water quality and stream functionality, it will be important that these alternative methods of flood control be utilized. Converting natural streams to storm sewers is an unenlightened way to address flooding problems.
Quantify the effects of stream hardening on water quality and stream functionality and the effects on the near shore coral ecosystem.
NOAASupplemental:Entry_ID: UnknownSensor_Name: water quality sensorsProject_Campaign: Hawaii Coral Reef InitiativeOriginating_Center: Department of Oceanography, University of Hawaii at ManoaStorage_Medium: MS Excel, MS Word, CSV ASCII, ASCII TEXTOnline_size: 6152 Kbytes Resource Description: NODC Accession Number 0001070
ground condition
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quality control complete
standard methods
Waimanalo Stream was sampled along the Kahawai tributary and below the confluence of Kahawai and Waimanalo Streams near the mouth of the stream where it discharges into Waimanalo Bay. Most of the Waimanalo Stream stations were sampled a total of 10-12 times at roughly 3-4 week time intervals during the period February-October, 2002. Kaneohe Stream sampling was carried out at roughly three-week intervals during the period June-November, 2002. Most Kaneohe Stream stations were sampled a total of nine times. Waimanalo stations 2-5 and 7 lie along a hardened section of the stream that extends for a distance of approximately 0.8 km upstream and immediately downstream of Kalanianaole Highway. Station 1 lies immediately upstream of the hardened section. Station 6 is the effluent from an underground storm sewer that discharges beneath the Kalanianaole Highway bridge. Stations 7-9 lie at the beginning, midpoint, and end, respectively, of a stream restoration project carried out by the Waimanalo Watershed Project. Station 10 is at the head of the Waimanalo Stream estuary. In the Kaneohe Stream study, station 1 is located in a natural stream channel with no upstream hardening. Station 5 is the effluent from a spring that seeps into Kamooalii Stream near the Likelike Highway culvert. Station 10 is immediately downstream of the hardened section of the stream in the head of the Kaneohe Stream estuary. The remaining stations are located along the hardened section of Kamooalii/Kaneohe Stream. Water samples were collected in 250-ml plastic bottles and immediately placed in an ice chest. Measurements of temperature, pH, oxygen concentration, and turbidity were made in the field. Temperature was recorded to the nearest 0.1oC with a thermometer calibrated at 0oC (ice bath) and 100oC (boiling water). Oxygen concentrations were recorded with a YSI model 58 dissolved oxygen meter. pH was recorded to the nearest 0.1 using an IQ Scientific model 3000 portable pH meter. In the laboratory, the water samples were filtered through pre-weighed glass fiber filters (Whatman GFF) with a nominal porosity of 0.7 ?m. The filters were dried in a drying oven at 105oC to constant weight. The filters were weighed on a Mettler model H20T analytical balance to the nearest 0.01 mg. Duplicates were run on random samples as a check on precision. Blanks were run by filtering 250 mL of distilled water through a filter. The weight of material collected on the filters ranged from a few milligrams to several tens of milligrams. The blank correction was less than 0.1 mg. The concentration of total suspended solids (TSS) was calculated from the difference in the weights of the filter before and after filtering. The filtrate from the suspended solids filtration step was transferred to plastic bottles and processed for nutrient concentration measurements. The filtrates were frozen if not immediately analyzed. Concentrations of nitrate + nitrite (hereafter, nitrate), phosphate, and silicate were measured on the filtrate using colorimetric techniques on a Technicon Instruments AutoAnalyzer. The procedures used for the colorimetric assays adhered to those described in APHA (1998). Limits of detection were 0.5 ?M for silicate and 0.1 ?M for nitrate and phosphate. Concentrations of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) were determined by first oxidizing the filtrates with an Ace-Hanovia ultraviolet light photo-oxidation unit and then assaying for nitrate and phosphate, respectively. Concentrations of particulate nitrogen (PN) and particulate phosphorus (PP) were calculated by assuming that the TSS contained 0.35% nitrogen and 0.11% phosphorus byweight (Laws and Ferentinos 2002). Concentrations of total nitrogen (TN)and total phosphorus (TP) were then calculated as TDN + PN and TDP + PP,respectively.
Data received in MS Excel and MS Word. RedundantASCII copies were made of each as CSV or TXT format.1) Directory: data/excelFILENAMESHCRIdata.xlsHCRIdata_Kaneohe.csvHCRIdata_waimanalo.csvFORMATS:xls: MS Excelcsv: ASCII Comma-Separated-format; redundant copy of each sheetCONTENTData files (Columns defined in each file or sheet)2) Directory: data/reportFILENAMESHCRImaps.docfigure1.jpgfigure2.jpgFORMATS:doc: MS WORDjpg: jpeg plotCONTENTS:Maps of station locations. Figures in HCRImaps.docwere printed then scanned into the two JPG filesFILENAMESnoaareport.docnoaareport.txtFORMATS:doc: MS WORDtxt: ASCII copyCONTENTS:Complete report
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