Hydrological, chemical and biological assessment of two New Mexico headwater streams (2023)

Headwater streams play a crucial role in arid and semiarid regions. They provide freshwater to adjacent lowlands and temporarily store water as snowpack and groundwater. Downstream users – both humans specifically and ecosystems more broadly – depend on the delayed release, particularly during dry seasons. Headwater streams are highly vulnerable to climate change through shifts in snowmelt dynamics, changes in precipitation, evapotranspiration, and wildfire prevalence, among other factors. Monitoring headwater streams in dryland areas over time is therefore of critical importance.

Each year, graduate students enrolled in the Water Resources Program at the University of New Mexico monitor hydrological, chemical, and biological characteristics of two headwater streams in central New Mexico as part of a field methods class. This dataset contains measurements from the 2023 field campaign. At each stream site, measurements were repeated for three separate transects.  

Las Huertas Creek (LH), the first monitoring site, is the only perennial stream in the Sandia Mountains. The stream drains north from the northeastern slope of the Sandias towards the town of Placitas, running through a narrow and heavily forested canyon. Transects range in elevation from 2190 m – 2320 m above sea level and were sampled on September 30, 2023. The second monitoring site is on the East Fork of the Jemez River (JR) within the Valles Caldera National Preserve. The stream runs through montane grasslands of the caldera, a 20 km circular depression formed by a large volcanic eruption and subsequent land subsidence approximately 1.2 million years ago. Transects are located at an elevation of approximately 2560 m above sea level and were sampled on October 7, 2023.

Methods
Discharge and Sediment
Discharge at each transect was estimated using two methods: (1) the velocity-area method, with velocity measured using a Marsh-McBirney Flow-Mate Model 2000 flow meter, and (2) the salt dilution (or dry injection) method after Hudson and Fraser (2005). Electrical conductivity (EC) for the salt dilution method was monitored in 5-second increments using a YSI Professional Plus multiparameter meter, and in 1-second increments using an Arduino-based EC probe and datalogger built as part of the class. Particle size distribution of the channel bed surface was characterized based on the pebble count method (Wolman, 1954) by randomly selecting 100 pebbles along a zig-zag pattern (Bevenger and King, 1995) and measuring them with a gravelometer. In addition to the pebble count, a grab sample (approximately 500 g) of stream sediment was collected with a trowel at each transect and subjected to sieve analysis based on ASTM D6913 (ASTM, 2009).

Water Chemistry
The following water chemistry parameters were measured at one central location per transect: temperature (°C), conductivity (µS/cm), specific conductivity (µS/cm), pH, and dissolved oxygen (mg/L and %). The parameters were measured with a YSI Professional Plus multiparameter meter. Turbidity (NTU) was also measured at one central location per transect using a Hach 2100P portable turbidimeter.

Water samples were taken to measure alkalinity in a lab environment; approximately 50 mL of unfiltered water was collected at one location per transect and placed in a centrifuge tube, which was stored under refrigeration until lab testing. Alkalinity was determined by using endpoint titration; the titrant was 0.02 N sulfuric acid, while indicator solutions used were phenolphthalein (for carbonate) and bromocresol green (for bicarbonate).

Additional water samples were collected to test the anion and cation concentrations in a lab environment. At one central point per transect, approximately 50 mL of water was collected, filtered through a 0.45 µm glass fiber filter, and stored in a 50 mL centrifuge tube. A few drops of dilute nitric acid were added to only the cation samples, while nothing was added to the anion samples. All samples were stored under refrigeration until lab analysis. Cation concentrations were analyzed using inductively coupled plasma-optical emission spectroscopy (ICP-OES) with a PerkinElmer Optima 5300DV. Anion concentrations were analyzed using ion chromatography (IC) with a Dionex 1100 IC.

Organic Matter and Benthic Macroinvertebrates
Organic matter was qualitatively sampled from three points (left bank, center, right bank) at each transect.  Substrate was collected with a trowel while samples from the water column were collected in one liter Nalgene bottles.  In the lab, water and substrate samples were processed for Ash Free Dry Mass (AFDM) (Steinman et al., 2017). The water samples were filtered through a 1.5 µm glass fiber filter. The filters and substrate samples were dried for 24 hours at 60°C, weighed, ashed at 500°C for 4 hours in a muffle furnace and reweighed. The difference in the weights was calculated as the % organic matter as AFDM.

Aquatic macroinvertebrates were collected from a known area (measured in m2) at each transect using a D-frame net. Samples were preserved in 70% ethanol and stored in whirlpak bags.  In the lab, invertebrates were separated from organic/inorganic matter using forceps and a dissecting microscope, enumerated, and identified to Order (in most cases), using taxonomic references including Voshell (2002). Macroinvertebrate densities were calculated from raw counts as individuals/m2.

References
ASTM, 2009. Standard test methods for particle-size distribution (gradation) of soils using sieve analysis. ASTM D6913-04(2009)e1. West Conshohocken, PA.
Bevenger, G.S., 1995. A pebble count procedure for assessing watershed cumulative effects (Vol. 319). US Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO.
Hudson, R. and Fraser, J., 2005. The mass balance (or dry injection) method. Streamline Watershed Management Bulletin, 9(1), pp.6-12.
Steinman, A.D., Lamberti, G.A., Leavitt, P.R., and D.G. Uzarski. 2017. Biomass and pigments of benthic algae, pp. 223-241 in (Hauer, F.R. and G.A. Lamberti eds) Methods in Stream Ecology: Vol. 1 Ecosystem Structure, Third Edition. Academic Press, Cambridge, MA.
Voshell, J.R., 2002. A Guide to Common Freshwater Invertebrates of North America. University of Nebraska Press, Lincoln, NE.
Wolman, M.G., 1954. A method of sampling coarse river‐bed material. EOS, Transactions American Geophysical Union, 35(6), pp.951-956.