DATA SET IDENTIFIER: Rio Icacos hyporheic and riparian chemistry

PROJECT TITLE: Riparian Carbon and Nitrogen Dynamics

PROJECT DESCRIPTION: Hydrologic and chemical characteristics were determined for both riparian and hyporheic subsurface flow along a 100-m reach of a sandy-bottom tributary of the Rio Icacos in the Luquillo Experimental Forest, Puerto Rico. Hydrologic data (vertical hydraulic gradient and hydraulic conductivity of streambed sediments) and the topographic and morphological features of the watershed indicated diffuse inputs of groundwater from the near-stream riparian zone along this site. Cumulative groundwater discharge, determined by tracer dilution techniques, was ~1.5 L/s or 10% of the total stream discharge. Spatial heterogeneity in hydrologic and chemical properties of riparian and hyporheic sediments was large. Hydraulic conductivity explained much of the variation in NH₄-N and dissolved organic carbon (DOC) concentrations, with highest concentrations in sites having low conductivity. A mass-balance approach was used to examine the influence of the near-stream zone on nutrient transport and retention. Outwelling riparian groundwater had the potential to increase stream N concentrations by up to 84% and DOC concentrations by up to 38% along our 100-m reach. Because stream concentrations were constant downstream despite this input, we conclude that significant N and C retention or loss were occurring in the near-stream zone. Lotic ecosystems and their associated riparian groundwater can have a quantitatively significant impact on the nutrient budgets of tropical headwater catchments.

LTER CORE AREAS: (Annotate all that apply)

Inorganic inputs and nutrient movement

LEF LTER 1 RESEARCH TOPIC: (Annotate all that apply)

Environmental monitoring

We define a data file as a component of a data set. A data set can have only one data file or more. Basically, different data files have different data structures or format.
DATA SET FILES (SUBSETS):

Data File No.	Data File Identifier	On-Line Filename	Starting Date	Periodicity of sample	End Period
1	Hyporheic chemistry	hypchem.txt	6/8/96	Weekly	7/26/96
2	Sample name description	hypname.txt	N/A	N/A	N/A

RESEARCH LOCATION: Third tributary on the left upstream from the USGS weir on the Rio Icacos in the Palo-colorado forest zone

INVESTIGATORS:

PRINCIPAL INVESTIGATORS E-MAIL address

William H. McDowell

Bill.McDowell@unh.edu

OTHER RESEARCHERS E-MAIL address

Tamara Chestnut

tjeklund@christa.unh.edu

CONTACT PERSONS E-MAIL address Phone Number (Include area code)

William H. McDowell	Bill.McDowell@unh.edu	(603)862-1020
Tamara Chestnut	Tami.Chestnut@unh.edu	(603)862-2341

SOURCE OF FUNDING (SPONSOR): NSF grant to the Terrestrial Ecology Division, University of Puerto Rico and the International Institute of Tropical Forestry as part of the Long-term Ecological Research Program in the Luquillo Experimental Forest.

DATA SET ABSTRACT: Same as project description

DATA SET METHODS: Groundwater and hyporheic wells. Six well transects were installed along the 100-m stream reach. Floodplain wells were placed along transects on both sides of the stream at ~1 and 10 m from the stream. Floodplain wells were made of 5-cm PVC with 61 cm of slotted well screen that was covered with polyethylene geotextile fabric filter to reduce particle infiltration and clogging of screens. Well screens for riparian wells ranged from 1 to 3 m in depth depending on location. Hyporheic wells were installed at each transect as 3 sets of vertically nested wells located on the left, center, and right sides of the stream. Hyporheic wells were installed at depths of 10, 30, 50, and 80 cm below the ground surface with each nest oriented longitudinally along the stream. Hyporheic wells were made of 2.5-cm PVC pipe with 5-cm perforated well screens. Wells were capped on the bottom and were limited to 10 cm of pipe below the screen.

Hydrologic characteristics. Hydraulic conductivity was measured during baseflow conditions using a bail-mode test. All water was evacuated from the well, and the time required for the water level to return to pre-bail conditions was closely monitored and calculated following the Hvorslev (1951) method (Freeze and Cherry 1979). A shape factor was required for estimation of K for hyporheic wells because of the reduced length of the well screen (5 cm) used for vertical characterization (Cedergren 1989). The shape factor adjusts Hvorslev’s calculation to account for wells designed for point measurements.

Chemical sampling.--- Samples were taken from all wells and from stream water on 6 sampling dates from June 1996 to August 1996 under baseflow conditions. A stage height of 1.2 m or lower on the gage at a USGS weir (Station 50075000) located several hundred meters downstream of the tributary outlet on the mainstem of the Rio Icacos, along with stream height measurements along the tributary, indicated approximate baseflow conditions for sampling. All wells were bailed dry and allowed to refill 1 d prior to sample collection. Samples were filtered using pre-combusted Whatman GF/F 0.7-m m filters within 24 h of field collection. A 3-mL subsample for anion analysis was filtered with a 0.22-m m Acrodisc filter and refrigerated prior to analysis. All other samples were frozen in acid-washed polyethylene (HDPE) bottles. Dissolved O₂ (DO) measurements were made with a YSI handheld O₂ meter (Model 55).

Chemical analysis.--- Nitrate, Cl^-, and SO₄-S were analyzed using high-performance liquid chromatography (HPLC) with a Dionex self-regenerating suppressor (4-mm), Ionpac AS4A (10-32) analytical column, Waters 431 conductivity detector, and a photo-diode array detector set to a wavelength of 214 nm for UV detection of NO₃-N. Ammonium-nitrogen was analyzed by flow injection analysis colorimetry (Lachat) with the phenol hypochlorite method and sodium nitroprusside enhancement. A total organic C analyzer (Shimadzu TOC 5000) with acidification and sparging was used for measuring non-purgeable organic carbon (NPOC), which excludes highly volatile organic compounds from the dissolved organic carbon (DOC) measurement. NPOC is commonly referred to as DOC in both freshwater and marine ecosystems (Sharp et al. 1993). High-temperature catalytic oxidation (Shimadzu TOC 5000) with chemiluminescent N detection (Antek 720) was used to analyze total dissolved N (TDN, Merriam et al. 1996); dissolved organic N (DON) was estimated by the difference between TDN and NH₄-N + NO₃-N.

REFERENCES:
McDowell, W.H. and C.E. Asbury. 1994. Export of carbon nitrogen and major ions from three tropical montane watersheds. Limnology and Oceanography 39: 111-125.

Boccechiamp, R.A. 1977. Soil survey of Humacao area of eastern Puerto Rico. United States Dept. of Agriculture Soil Conservation Service, San Juan, Puerto Rico. US Government Printing Office, Washington, DC.

Hvorslev, M.J. 1951. Time lag and soil permeability in groundwater observations. US Army Corps of Engineers, Waterways Experimental Station Bulletin 36. US Army Corp of Engineers, Vicksburg, Mississippi.

Freeze, R.A. and J.A. Cherry. 1979. Groundwater. Prentice-Hall, Englewood Cliffs, New Jersey.

Sharp, J.H., R. Benner, L. Bennett, C.A. Carlson, R. Dow, and S.E. Fitzwater. 1993. Re-evaluation of high-temperature combustion and chemical oxidation measurements of dissolved organic carbon in seawater. Limnology and Oceanography 38: 1774-1782.

Merriam, J., W.H. McDowell, and W.S. Currie. 1996. A high-temperature catalytic oxidation technique for determining total organic nitrogen. Soil Science Society of America 60: 1050-1055.

CROSS-REFERENCES (other data sets related to this one):

SAMPLE LOCATION: All samples were stored and analyzed at Ecosystem Analysis Laboratory at the University of New Hampshire, Durham, NH 03824

STORAGE SITES (of data files): William H. McDowell, Department of Natural Resources, 215 James Hall, University of New Hampshire, Durham, NH 03824; ITES' Data Management files DM-002, Drawer #4

INVESTIGATOR'S ASSIGNED KEYWORDS: tropical rainforest, nutrient cycling, nitrogen, DOC, riparian zone, hyporheic zone, hydrologic characteristics

LEF LTER OFFICIAL KEYWORDS (See table): Q ICACOS, COLORADO, RIPARIAN, RIVER, PEER REVIEWED JOURNAL

PUBLICATIONS:
Chestnut, T.J. and W.H. McDowell. 2000. C and N dynamics in the riparian and hyporheic zones of a tropical stream, Luquillo Mountains, Puerto Rico. J. N. Am. Benthol. Soc. 19(2): 199-214.

DISSEMINATION: UNRESTRICTED

REASONS TO RESTRICT DATA IN THIS DATA SET BEYOND ITS TWO YEAR POLICY PERIOD*:

*WILL HAVE TO BE APPROVED BY LTER PRINCIPAL INVESTIGATORS: J. ZIMMERMAN, A. LUGO , D.J. LODGE

FILING
___ "File" copy only : Data Management will only file an electronic copy of the data file and its documentation
X "Enter" data on-line : Data Management will be in charge of entering the data on computer files (Contact Eda C. Meléndez)

SITES DESCRIPTIONS: Third tributary on the left upstream from the weir on the Rio Icacos in the Palo-colorado forest zone. Samples were collected from riparian groundwater wells, hyporheic wells, and the stream.

Geographical positional system (GPS) Coordinates for each location:

location	latitude	longitude
Rio Icacos left upstream third tributary

VARIABLES (ATTRIBUTES):

FILE NAME OR #ABOVE (all in which the variable appears)	1, 2	1	1	1	1	1
ABBREVIATION (as it appears on the data file)	Sample	Date	NO3N	NH4N	DON	TDN
NAME OF VARIABLE	Name of sample location	Collection date	Nitrate-N	Ammonium-N	Dissolved organic nitrogen	Total dissolved nitrogen
DEFINITION OF VARIABLE	Name of sample location: site number and well or stream	Date of collection of sample	Nitrate-N	Ammonium-N	Dissolved organic nitrogen	Total dissolved nitrogen
UNIT		milligramsPerLiter (mg/L)	milligramsPerLiter (mg/L)	milligramsPerLiter (mg/L)	milligramsPerLiter (mg/L)	milligramsPerLiter (mg/L)
PRECISION			0.01	0.01	0.2	0.1
RANGE OR LIST OF VALUES		06/08/1996 to 07/26/1996	0 to 0.46	0 to 5.79	0 to 0.77	0 to 5.95
DATA TYPE	alphanumeric	date	decimal	decimal	decimal	decimal
MISSING DATA CODES	blank	blank	blank	blank	blank	blank

VARIABLES:

FILE NAME OR #ABOVE (all in which the variable appears)	1	1	1	1	1
ABBREVIATION (as it appears on the data file)	DOC	SO4S	CL	KSAT	DO
NAME OF VARIABLE	Dissolved organic carbon	Sulfate-s	chloride	Saturated hydraulic conductivity	Dissolved oxygen
DEFINITION OF VARIABLE	Dissolved organic carbon	Sulfate-s	chloride	Saturated hydraulic conductivity	Dissolved oxygen
UNIT	milligramsPerLiter (mg/L)	milligramsPerLiter (mg/L)	milligramsPerLiter (mg/L)	centimetersPerSecond (cm/s)	milligramsPerLiter (mg/L)
PRECISION	0.1	0.01	0.01	0.01	0.1
RANGE OR LIST OF VALUES	0 to 11.3	0 to 1.13	0 to 20.94		0.28 to 5.85
DATA TYPE
MISSING DATA CODES	blank	blank	blank	blank	blank

VARIABLES:

FILE NAME OR #ABOVE (all in which the variable appears)	2	2
ABBREVIATION (as it appears on the data file)	CODE	DESCRIPTIONofCODE
NAME OF VARIABLE	Site, well or stream code	Description of code
DEFINITION OF VARIABLE	Site, well or stream code	Site name of location and description of well or stream
UNIT	N/A	N/A
PRECISION	N/A	N/A
RANGE OR LIST OF VALUES	10A, 10B, 10C, 30A, 30B, 30C, 50A, 50B, 50C, 80A, 80B, 80C, F10A, F10C, F1A, F1C, S10, S11, S4, S5, S6, S7, S8, S9, STREAM
DATA TYPE	alphanumeric	alphanumeric
MISSING DATA CODES	none	none

COMPUTATIONAL METHODS:

Variable Name	Formula
DON	DON = TDN – (NO3N + NH4N)

FOR DATA MANAGER USE ONLY

DATE OF LAST REVIEW: September 30, 2004
DATE OF LAST ENTRY: Jul 26, 1996
STAGE OF DATA SET MANAGEMENT (dates):
RECEIVED ENTERED: Oct 2000 Feb 2001
FILED ON-LINE: Feb 7, 2001
REVIEWED BY RESEARCHER
FILING MEDIA:
NAME OF DOCUMENTATION FILE: lterdb109.htm
NAME OF ON - LINE CATALOG: LTERDBAS
RECORD #: 109
DOCUMENT TYPE: magnetic media only
PRIORITY TO BE ENTERED: N/A

Rev. date of this form: 8 June 2000 (updated Feb 6, 2001)