North Carolina Division of Water Quality



North Carolina Division of Water Quality

Surface Water Protection Section – Program Development Unit

Watershed Assessment Team

January 20, 2008

Lake Rogers and Little Ledge Creek Watersheds

Summary of Water Quality Data Collections

Neuse River Basin

Catalog Unit # 03020201

HU 03020201060010

I. Executive Summary

Five sites on Ledge Cr., L. Ledge Cr., and Holman Cr. in the upper Neuse River basin were selected for monitoring of chemical and physical parameters (dissolved oxygen, specific conductance, pH, water temperature, total suspended solids, ammonia, nitrite+nitrate, total Kjeldahl nitrogen, and total phosphorus). Sampling occurred four times between November 13 and December 8, 2008. No significant water quality issues were noted at any location. One site on Holman Cr. had lower dissolved oxygen levels and higher concentrations of some nutrients, but this can be attributed to the lentic nature of the site: it was located in the backwaters of Lake Rogers, and no flow was seen at any time during site visits. The only issue noted in this study was possible excessive sediment inputs in Ledge Cr. and L. Ledge Cr., based on visual assessments of the substrates. However, the levels of sedimentation in Ledge Cr. seemed to be less extensive than what is generally seen in Triassic Basin streams, as cobble and bedrock were present and the substrate was not entirely sand and silt.

II. Introduction

The Ecosystem Enhancement Program (EEP) requested that the NC Division of Water Quality (DWQ) Watershed Assessment Team (WAT) collect chemical water quality data in the Lake Rogers and L. Ledge Cr. watersheds in support of Phase IV activities of their local watershed plan (LWP) development. Little water quality data have been collected in this area in the past, likely due to poor flows due to backwater effects of Lake Rogers, beaver activity, the natural characteristics of streams in this ecoregion, and the presence of large riparian wetland complex in the watershed. (Monitoring methods for DWQ, such as instream chemistry and benthic macroinvertebrates, require flowing water for accurate interpretation.) The objective of the monitoring by WAT was to provide baseline instream nutrient and total suspended solids (TSS) levels for the two main tributaries feeding Lake Rogers (Ledge Cr. and Holman Cr.) and a tributary to Falls Lake (L. Ledge Cr.).

The area is located in the upper Granville Co. (Figure 1). This portion of the upper Neuse River basin is in the Triassic Basin ecoregion. The majority of area in the watershed is forested, though roughly a third of the land area is used for agriculture (row crops and pasture). There are small amounts of development around the community of Stem, along the I-85 corridor, and along a portion of the Lake Rogers shoreline. Riparian areas appeared to be well buffered by wetlands or forested areas except in the extreme upper portion of Ledge Cr. and Holman Cr. A review of 2001 land use data (National Land Cover Database) and 2005 aerial photography indicated that agriculture with poor or non-existent buffers was prevalent in these areas.

|[pic] |

|Figure 1: Location of study area |

III. Methods

Five sites were selected for sampling: two each on Ledge Cr. and Holman Cr., and one location on L. Ledge Cr. (Table 1, Figure 2). No sites were sampled in or downstream of the lake since dredging began in fall 2008 and will continue through the winter. Sites were visited four times over a four-week period in November-December 2008. At each visit, field parameters (dissolved oxygen, pH, water temperature, specific conductance) were measured in situ using either a Hydrolab Quanta multiparameter meter, or a combination of a

|[pic] |

|Figure 2: Monitoring locations |

YSI 85 multiparameter meter and Fisher Accumet 61 pH meter. Water samples were collected and submitted to the DWQ Laboratory Section for analysis of ammonia nitrogen (NH3), nitrite + nitrate nitrogen (NO2+NO3), total Kjeldahl nitrogen (TKN), total phosphorus (TP), and total suspended solids (TSS). Sampling took place under baseflow conditions (defined as >48 hours since last measureable rain) except on the last sample run (Dec. 8), where 0.10” of rain fell 24-48 hours before. Digital photos and field notes were taken during each visit. The latitude and longitude for each site were recorded using a recreational grade GPS receiver.

Quality assurance and quality control (QA/QC) activities included calibration of field meters at the beginning and end of each day of sampling, and collection of duplicate samples from one site each day. Relative percent difference (RPD) was calculated for each set of duplicates to determine total variability due to all factors (environmental, sample collection and handling, and laboratory analysis).

More details on methods can be found in the monitoring plan (NC DWQ, 2008).

|Table 1: Monitoring location latitudes and longitudes (field collected) |

|Station number |Station description |Latitude |Longitude |

| | |(dd.dddd) |(dd.dddd) |

|HC1127 |Holman Cr at SR 1127 (Brogden Rd) |36.1367 |-78.6967 |

|HC1131 |Holman Cr at SR 1131 (Tump Wilkins Rd) |36.1831 |-78.7098 |

|LC1215 |Ledge Cr at SR 1215 (Lyon Station Rd) |36.1775 |-78.7139 |

|LC1004 |Ledge Cr at SR 1004 |36.1951 |-78.7295 |

|LLC1724 |L Ledge Cr at SR 1724 (Northside Rd) |36.0919 |-78.7241 |

IV. Results

A. Site descriptions

Holman Cr. at SR 1127 (HR1127, Figure 3) was the downstream location on Holman Cr., with a drainage area of approximately 9.5 mi.2. Instead of a flowing stream, the creek is essentially the backwaters of Lake Rogers at this point, and it was stagnant and slightly tannic. No flow was seen at this location during any of the site visits. Riparian areas appeared to be intact forest.

|[pic] |

|Figure 3: Site HC1127, Holman Cr. at SR 1127 (Brogden Rd.) |

Holman Cr. at SR 1131 (HC1131, Figure 4) was upstream of HR1127 and had a small drainage area (1.8 mi.2). This site was severely impacted by beaver impoundments but there was visible flow- though extremely low- during most site visits.

|[pic] |

|Figure 4: Site HC1131, Holman Cr. at SR 1131 (Tump Wilkins Rd.) |

Ledge Cr. at SR 1215 (LC1215, Figure 5) was the downstream site on Ledge Cr. It was fairly small, with a wetted channel width of approximately 2 m and a drainage area of 3.4 mi.2. The substrate was extremely sandy and mid-channel bars indicated that it is actively aggrading. Flow was generally good or excellent where sampled downstream of the road, though upstream was impounded by a debris jam at the culvert. The water was generally very clear. The riparian areas were relatively young intact forest.

|[pic] |

|Figure 5: Site LC1215, Ledge Cr. at SR 1215 (Lyon Station Rd.) |

Ledge Cr. at SR 1004 (LC1004, Figure 6) was the upstream site on Ledge Cr. The drainage area at this location was 1.8 mi.2 and the wetted channel width was slightly smaller (1.5-2m) than downstream at LC1215. Also similar to downstream, the substrate at this location was predominantly sand, though some cobble and bedrock were present as well. Flow was consistently good at this location. Heavy filamentous algae and periphyton growth were observed.

|[pic] |

|Figure 6: Site LC1004, Ledge Cr. at SR 1004 |

L. Ledge Cr. at SR 1724 (LLC1724, Figure 7) was not hydrologically connected to the Ledge Cr. or Holman Cr. watersheds, but instead drains directly to Falls Lake. Though it had a small drainage area (2.6 mi.2), the channel was quite wide (approximately 6-7m) and generally shallow (48 hours since last |

| | |measureable rain; “Other” as measureable rain occurred in|

| | |the previous 48 hours, but not during sampling |

| | |activities. |

|[pic] |[pic] |[pic] |

|[pic] |[pic] | |

| | | |

| | | |

| | |Figure 9: Analytical results by |

| | |monitoring site 1 |

| | |[pic] |

| | | |

| | |1 “Baseflow” is defined as >48 hours since last |

| | |measureable rain; “Other” as measureable rain occurred in|

| | |the previous 48 hours, but not during sampling |

| | |activities. |

C. Quality assurance and quality control (QA/QC)

All pre- and post-sampling calibrations of field meters were within tolerances specified by DWQ standard operating procedures (NC DWQ, 2006).

The relative percent difference (RPD) calculated for each set of duplicate samples and overall means RPD by parameter are shown in Table 2. There were a large percentage of duplicate samples where both results were reported as less than the reporting limit (ND). RPD was not calculated in these cases, since the reported result is a “less than” value. Unfortunately, this problem was widespread for certain parameters, and so little useful QA information is provided by this data set. One set of duplicates collected November 13 suggest that total variability from all sources for TP and TSS may be quite large; this may have serious implications if analytical results are to be compared to any benchmark values or if inter-site comparisons are made. Results from other sample sets show little or no variability for NH3, TKN, and TP.

|Table 2: Relative percent differences (RPD) from duplicate samples |

|Date |Station number |NH3 |NO2 + NO3 |TKN |TP |TSS |

|11/13/2008 |LLC1724 |-- 1 |-- 1 |6% |77% |71% 2 |

|11/19/2008 |HC1127 |0% |-- 1 |0% |0% |-- 1 |

|12/3/2008 |LC1004 |0% |0% |4% |0% |-- 1 |

|12/8/2008 |HC1131 |-- 1 |-- 1 |7% |0% |-- 1 |

| |Mean: |0% |0% |4% |19% |71% |

|1 No RPD was calculated as both results were non-detects. |

|2 One result was reported as a non-detect; the detection limit was used as the value for RPD calculation. |

V. Discussion

The data collected on Ledge Cr., L. Ledge Cr., and Holman Cr. are difficult to interpret, as there were only four sets of samples collected over a short period of time. Poor flow at some sites also complicates data interpretation, particularly the two Holman Cr. sites which were impounded by Lake Rogers and beaver activity. It should also be noted that since there were very few samples taken over a very short period of time, results cannot be extrapolated beyond the “snapshot” that they represent. There are likely seasonal or other effects on instream water quality that were not addressed with this sampling design.

In general, no major water quality concerns were noted at any sites that could not be explained by impoundment of the waterbodies. Visual assessments, however, indicate that excess sediment may be an issue in Ledge and L. Ledge Cr., though this is fairly typical of streams in the Triassic Basin ecoregion. The levels of sedimentation in Ledge Cr. may actually be slightly better than generally seen in Triassic Basin streams, as cobble and bedrock were present and the substrate was not entirely sand and silt.

VI. References

Griffith, G.E., Omernik, J.M., Comstock, J.A., Schafale, M.P., McNab, W.H., Lenat, D.R., MacPherson, T.F., Glover, J.B., and Shelbourne, V.B. 2002. Ecoregions of North Carolina and South Carolina. U.S. Geological Survey. Reston, Virginia.

NC Division of Water Quality (DWQ). 2006. Intensive Survey Unit Standard Operating Procedures Manual: Physical and Chemical Monitoring, Version 1.3. Environmental Sciences Section. Raleigh, NC.

NC DWQ. 2008. Water Quality Monitoring Plan for Ledge, Little Ledge, and Holman Creeks. Wetlands and Stormwater Branch, Wetlands Program and Policy Development Unit, Watershed Assessment Team. Raleigh, NC.

Appendix 1: Water Quality Data

The following table includes all raw data collected during this monitoring effort. For sites/dates with more than one set of analytical results (NH3, NO2+NO3, TKN, TP), these are the results from duplicate samples. Analytical results shown with a “ ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download