1. Missouri Nutrient Criteria Development
Mark Osborn
The current nutrient criteria plan for Missouri calls for development of nutrient criteria for lakes and reservoirs this year, and for streams in Most of today's talk will be devoted to where we are on lakes and reservoirs.

2. Lakes & Reservoirs Natural Lakes (very few)
Sinkhole ponds (in karst areas)
Ox-bow lakes, blew holes, wetland lakes
1 tectonic
Artificial Lakes and Reservoirs
~2900 > 5 ac in area
22 > 1000 ac in area
456 listed as Waters of the State
Since 1976, professors Jack Jones and Matthew Knowlton of the University of Missouri have been collecting data from many of the lakes and reservoirs throughout the state. Parameters include total nitrogen, total phosphorus, Chlorophyll-a, Secchi Depth, and volatile and non-volatile suspended solids. In 2003, they provided our agency with a lengthy assessment of the characteristics of the lakes, but they stopped short of recommending numerical nutrient criteria. Much of the report was devoted to describing a morphological overview.
(click) - There are very few natural lakes in Missouri. They include sinkhole ponds, ox-bow lakes, blew holes, and wetland lakes in the Missouri and Mississippi River bottomlands, and at least one tectonic lake.
(click) - The overwhelming majority of lakes in the state are artificial, and include an undetermined number of small ponds, about 2900 that are larger than 5 acres and 22 that are over 1000 acres.
(click) - Classified lakes that qualify as waters of the state are those that cross property boundaries, and there are 456 listed in the state regulation.

3. History of Reservoir Construction in Missouri (reservoirs > 10 acres in surface area)
Year Completed No. of reservoirs Percentage 1800 – – – – –
Most of the lakes and reservoirs in Missouri were built within the last hundred years. Since these are artificial environments, determination of what constitutes a reference condition is problematic. In situations such as this, EPA’s Technical Guidance Manual for Lakes and Reservoirs recommends the lake population distribution approach. Basically this means identifying the 25th percentile for each variable as the reference value (or 75th percentile in the case of Secchi Depth).
This plan may work as a starting point for identifying our benchmarks, but there are other factors to consider before we utilize this approach.

4. The trophic state of lakes and reservoirs in Missouri is highly variable, and considerably influenced by land cover within the watersheds. Oligotrophic lakes such as this one are usually surrounded by woodland.

5. While highly eutrophic waterbodies such as this may be impacted by point source discharges within the watershed, high applications of fertilizer on row cropping operations, and geese.

6. Lake Regions in Missouri
(12)
(53)
(82)
Given the high variability of lake population, size and morphological characteristics within previously delineated ecoregions, Jones and Knowlton made the determination that the most practical geographic approach in classifying lakes for nutrient management is to divide the state into three broad regions, the plains, the Ozarks and the Big River regions. This delineation is based largely on distinctions in underlying geology and surficial materials.
The plains region includes the central dissected till plain in the north and the Osage plain in the west. Bedrock geology is predominantly limestone and shale, overlain by glacial till in the north and bedrock residuum in the west. Ozark geology is dominantly limestone and dolomite, with some areas of igneous rock and sandstone. The Big River region consists of the flood plains of the Mississippi and Missouri, as well as the lower part of the Grand River.
The numbers to the right of the legend on this map refer to how many lakes and reservoirs in each region are included in the data set from which we are developing our nutrient criteria.

7. Range of Total Phosphorus samples in lake regions
Within each of the lake ecoregions, there is a wide range of nutrient concentrations in lakes, as indicated by this box plot. It includes all data points for phosphorus taken between 1976 and It is also evident that, despite some overlap, the data statistically supports the delineation of the three lake ecoregions.
The Ozark region is the most pristine, and includes all the oligotrophic and about two thirds of the mesotrophic lakes and reservoirs identified in the (b) report. This is reflected in the generally lower concentrations of total phosphorus identified in the right hand box.
The plains region, with more open land and more intense agricultural activity, includes lakes that range from mesotrophic to hyper-eutrophic conditions. Total phosphorus data is represented in the left hand box.
Most lakes in the Big River region are hyper-eutrophic, due to a combination of generally shallow morphology, slow flushing, and occasional flooding recharge which includes a high nutrient load. The box in the center reflects that situation.

8. Log distribution of Total Phosphorus in Lake Regions
Within each of the lake regions, log transformed data for total phosphorus distributes into a statistically normal curve, and these curves are distinct from each other. The violet columns are for Ozark lakes, the red columns for the plains, and the off white are for the Big River region. The differences in column height between the three groups are a reflection of the quantities of data from each region, which in turn is a reflection of the number of lakes and reservoirs within each region.

9. Log distribution for Total Nitrogen in Lake Regions
This trend holds up as well in the data distributions for total nitrogen..

10. Log distribution for chlorophyll-a in lake regions
And chlorophyll-a.

11. Log distribution for Secchi depth in lake regions
But it starts to fall apart a little when examining data for Secchi Depth. A probable factor is that reduction of lake clarity is not always a result of nutrient loading. In the plains and big river regions, suspended solids are frequently the principle cause of high turbidity, which can limit light for algae growth.

12. Median chlorophyll-a response to median total phosphorus
This is reflected in the cause and response modeling between total phosphorus and chlorophyll-a. The data points on this graph are from median values from each lake in the data set.
While chlorophyll concentrations are higher in the plains and big river regions, as expected, the slope of the trend lines and the response correlation are somewhat less than they are in the Ozarks, where nutrient concentrations are lower.

13. Potential TP criteria based on chlorophyll-a response (ug/L)th
percentile) TP a
(median)
Plains
8.2
22.5
15.4
43.9
Big Rivers
24.8
70.3
42.7
130.7
Ozarks
2.8
10.9
6.3
19.8
All other things being equal, if we were to base our phosphorus criteria on the response curve of the previous graphs, potential results are presented here. The figures for total phosphorus in the second column are somewhat lower than the actual 25th percentiles of phosphorus in the plains and big river regions, and about equal with it for the Ozarks region.

14. Other factors to consider
Designated Uses
Area, Depth, and Volume
Watershed size and characteristics
Residence time
But, of course, all other things are not equal. Within each of the lake regions, the lakes and reservoirs have a wide variations in characteristics that affect their response to nutrient loading. These include
(click) Designated uses. All the classified lakes and reservoirs are designated for supporting aquatic life, and virtually all are classified for whole body contact. However, maintaining the latter is not likely to be feasible in all areas, particularly in the plains and big river regions. In some situations, it may clash with support for aquatic life, where the clarity required for whole body contact would require nutrient levels to be too low to support aquatic life. Additionally 124 reservoirs are designated for drinking water supply. They will have special requirements to control taste and odor issues that result from nutrient loading.
(click) Lake dimensions. In our view, it doesn’t make sense for a 2,000 acre reservoir and a shallow five acre pond to be held to the same standard for nutrients.
(click) A lake is a reflection of it’s watershed. A lake in a large watershed dominated by cropland can not reasonably expected to achieve the same trophic status as a lake in a small watershed dominated by woodland. It has been shown that there is a direct correlation between the total phosphorus in a lake and the percentage of watershed that is in cropland.
(click)The other hydrologic factor, residence time.

15. Residence Time RT = 2 years RT = 1 years RT = .5 years outflow 50
inflow 50
Volume 100
RT = 2 years
outflow 100
inflow 100
Volume 100
RT = 1 years
Residence time is the inverse of flushing rate, and it can be roughly calculated from the other hydrologic factors. Generally, the longer the residence time for a lake, the higher tolerance that that lake has for nutrient loading, depending on other factors, such as percent cropland in the watershed.
outflow 200
inflow 200
Volume 100
RT = .5 years

16. Ultimately, the plan is to take all the factors that I have discussed here into account to develop a formula that will produce a reasonable estimate of the most appropriate bench mark for any given lake. All classified lakes will be grouped into discreet categories based on these considerations.

17. Streams
I am only going to touch briefly on our criteria development for streams. There are about 120,000 miles of stream in Missouri, of which about 22,000 have been classified for beneficial uses, including support for aquatic life.
Geographically, the Missouri Resource Assessment Partnership has delineated the state into 19 ecological drainage units, or EDU’s, based on distinctions of native aquatic life. DNR’s lab has identified 62 reference streams located in all but two of the EDUs. We have nutrient causal and response data for approximately half of these sites, and we will be collecting data on the rest over the next few years.
Nutrient criteria will then be developed based on the 75th percentile from these sites within the EDU’s.
Of course, once all this is done for both lakes and streams we have to proceed to the next phase which is...

18. Rule making procedures
Making rules. Here’s the process in Missouri. Got it? There’s going to be a quiz.
The right half of this chart describes processes that come after proposed rules are open to public comment. In order to expedite the process, the department has developed an ad hoc policy of involving stakeholders early on, before we jump through square 1 in the upper left hand corner.
All interested parties are invited to join the stakeholder group, and the nutrient criteria group has been meeting monthly since October. Participants include environmental groups, academics, municipalities, and agricultural interests. Our goal is to produce a draft rule for the next Clean Water Commission meeting in July. We don’t expect that it will have the unanimous support of the group. Dissenters will have an opportunity to present their position to the Commission as well.
The idea is that this will strengthen the case for the rule, in that potential issues with the rule can be anticipated before the public comment period.

19. Questions?