Nutrient Criteria Stakeholders Notes
April 18, 2006
USGS Conference Center
Columbia, MO
In Attendance: Greg Anderson, DNR-WPP; Georganne Bowman, DNR-WPP; Cindy DiStefano, MDC; Jack Dutra, JD Information Services; Peter Goode, Washington University; Candi Lordo, LMVP; Cassidy Luebbering, MEC Water Resources; Dan Obrecht, UMC; Mark Osborn DNR-WPP; Chris Riggert, MDC; Buffy Santel, St Louis MSD; Gary Welker, EPA Region VII; Tracey Winter, DNR-KCRO.
Mark Osborn: Our first speaker – Kristen will be unable to speak today. She had surgery recently – and now would not be a good time for her to present to the group. So, Dan will talk about Bootheel lakes and Sampling size.
Should Bootheel lakes be included in the Remnant River group?
Dan Obrecht (PowerPoint presentation)
The Bootheel or Mississippi Alluvial Plains Region encompasses five Missouri counties wholly and part of six others. With the exception of a few ridges, it is a flat region with elevation ranging from 240 – 335 feet above sea level. In the five counties that are totally within the region there are 16 classified lakes. MU has only sampled two of them, with water quality being quite different between these two lakes. Delaney Lake (a.k.a. Upper Big) has water quality that is similar to the oxbow data the group has looked at (TP >330 μg/L, TN >2000 μg/L, and chlorophyll >180 μg/L). In contrast, Big Oak Lake has water quality that is substantially better (TP ~40 μg/L, TN ~500 μg/L, and chlorophyll ~10 μg/L). Aerial photos of the two waterbodies help explain the difference; Delaney Lake looks like an oxbow that has had a small dam build to increase its size while Big Oak Lake is surrounded by forest (the lake might actually be best described as a cypress swamp?). Given the difference in water quality in these two lakes, it is difficult to know exactly how to categorize Bootheel waterbodies. Review of aerial photos indicate that other waterbodies in the region range from oxbows to wetland/marshes to geometrically shaped man-made reservoirs with unknown water sources to at least one “traditional” reservoir.
We may be able to group the obvious oxbows with the Big River Remnant Group (Gary) and some of the waterbodies may have to be considered when wetland criteria are developed (Mark). Dan is going to forward a list of MDC lakes in the region to Cindy who will try to gather more information on them.
Tracey noted that some of the Bootheel lakes may operate like some impoundments in the KC area that pump water from the river (no real watershed). She asked how nutrient criteria will be addressed in these situations.
Sample Size
Dan presented graphs showing the required sample size needed to achieve various levels of precision for estimating mean phosphorus concentrations during both spring-fall and summer periods (analysis was done following the approach of Marshall et al. 1988). This information was generated using data from six Missouri reservoirs that ranged from oligotrophic to hypereutrophic (unpublished MU data). For the spring-fall period, the number of samples required to achieve levels of precision of + 10%, + 15%, and + 20% of the mean were 13, 7, and 3, respectively. If sampling were limited to summer only, the number of samples needed to achieve these levels of precision would be 6, 3, and 2. The difference in required sample effort is a function of seasonal trends in water quality, in particular the higher variability that occurs in spring.
Nitrogen tends to fluctuate less than phosphorus in Missouri lakes, so fewer samples are required during the spring-fall period to achieve the above levels of precision. The required effort to estimate mean nitrogen levels during summer is the same as it was for phosphorus. Chlorophyll is more variable than either nitrogen or phosphorus, and therefore requires more samples (2-4 times more) to reach any given level of precision during both summer and spring-fall.
Dan noted that the minutes from the previous meeting needed to be corrected: it takes four years of data to generalize current water quality in Missouri lakes, not four years of data to detect trends. Depending on the natural variability of the lake and the intensity of the change in water quality, it could take 10-15 years to actually detect a statistically significant trend.
Mark asked about the required effort needed to estimate Secchi transparency. Dan responded that he had not analyzed sample requirements for Secchi transparency, but felt it would vary greatly depending on the waterbody. Eutrophic lakes could have chlorophyll that fluctuates greatly, but because the chlorophyll concentration is above the inflection point in the chlorophyll-Secchi relationship, the lake would show only small changes in water clarity. On the other hand, an oligotrophic lake might have minor fluctuations in chlorophyll levels, but because they occur near the inflection point of the chlorophyll-Secchi relationship, we would see large fluctuations in clarity and more Secchi readings would be needed to estimate the mean.
Marshall, C.T., A. Morin and R.H. Peters. 1988. Estimates of mean chlorophyll-a concentration: precision, accuracy, and sampling design. Water Resour. Bull. 24:1027-1034.
Large Reservoir – Spatial Variations
A series of maps with average TP values labeled were shown to convey how large reservoirs have longitudinal gradients. A challenge for the group is to determine how to compare tributary arms to each other, given that they have different hydrology and impacts. A graphic comparing soluble reactive phosphorus (SRP) values in the Kings River and James River arms of Table Rock Lake was shown to demonstrate the potential problems with comparing arms. The James River Arm had high SRP levels 30 miles up-lake from the confluence of the arm with the main lake. Values decreased and reached a level near zero around 20 miles from the confluence. The Kings River Arm is a shorter arm, and sampling only extended about 20 miles up the arm. SRP values were elevated at the 20 mile marker and decreased as sampling moved towards the confluence with the main lake (SRP values were still decreasing near the confluence). If both of these arms were sampled 10 miles from the confluence with the main lake one would think that the Kings River Arm (which had around 30 μg/L SRP at the 10 mile marker) was worse off than the James River Arm (which had near zero SRP at the 10 mile marker). While in reality, the upper James River Arm had approximately 50% more SRP than did the upper Kings River Arm (~150 vs. 100 μg/L).
Seasonal patterns in thermal stratification also affect the longitudinal gradients we find in large reservoirs. In winter, when the Table Rock Lake is mixed, inputs are slowly diluted out as they move down-lake. This results in an extended transition zone, with surface water quality changing over a fairly large distance. During the summer, when the lake is thermally stratified, inputs into the lake are cooler (and denser) than the lake water. Because of this difference in density, inputs plunge down and move through the middle of the water column. During summer the transition zone between lotic and lentic conditions is abbreviated, with changes in surface water quality occurring in a shorter distance relative to winter.
Proposed Matrix with Trophic Classifications.
Mark Osborn (handouts)
Several handouts were given to the group for review and discussion during the next meeting.
The handouts include:
Mark also wanted input from the group about some comments he received.
Dorris Bender supplied comments from the City of Independence. In her memo, she stated that other states have used narrative criteria instead of numerical criteria. Both Peter Goode and Gary Welker responded to her comments. Peter stated that permits are difficult to write and enforce with narrative criteria. Gary stated that numerical criteria is better when establishing the TMDL as well.
The second set of comments addressed the Big River Remnant lakes. The commenter stated that Yes historically these lakes were nutrient rich, due to the fact that frequent flooding would bring in high nutrient water. However, now that the lakes are cut off from the channel due to levees, most of the nutrients would be from agriculture. Therefore, BMPs could be used to clean-up an partically restore these waterbodies. Dan responded that there is probably a lot of internal loading in these lakes. During summer these lakes can stratify and phosphorus is released from the sediment when the bottom waters go anoxic. If the lake then mixes again, the phosphorus is mixed throughout the water column. Mark felt it was unlikely that the majority of these reservoirs receive runoff from agriculture
Follow-up tasks
Mark will set the next meeting date – first week in May (see below)
- Mark will send out the missing handout and provide the paper from Oklahoma which states the need for 10ug/l Chl-A value in drinking water. (Downing et al. 2001)
- Georganne will review document from Washington and report back to group
- Dan- send Bootheel lake list to Cindy for MDC input.
Next meeting Scheduled for May 2nd.
Lewis & Clark State Office Building
Jefferson City MO
1:00 to 4:00 p.m.
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