- Pond Productivity
- Drivers of Change
- Interactive Map
- HRUs
- Takeaways
Pond Productivity
The productivity of a pond is limited by the nutrients that are in a pond. These nutrients can enter the pond via the watershed or groundwater. In a freshwater system, the limiting nutrient is usually phosphorus, which means that the amount of algal growth in a lake is determined by the amount of phosphorus in the lake. However, there are other factors at play in these ecosystems that affect productivity, including the depth and volume of a pond, the residence time of the pond water (the amount of time water stays in a pond), the weather, and the mixing (or stratification) depth. The amount of production in a lake affects lake biology as a whole.
The trophic state index (TSI) is a measure of productivity, as reflected by abundance of algae. Per guidance from the North American Lake Management Society protocol (Carlson & Simpson, 1996), TSI is calculated from Secchi disk depth, chlorophyll a, or total phosphorus measurements. Given the availability of measured total phosphorus in previously collected Pond and Lake Stewardship program data, surface total phosphorus was used to calculate the Carlson TSI.
The trophic state index is rated on a scale from 0 to 100.
0–40: Oligotrophic
relatively low in plant nutrients, with abundant oxygen in the deeper parts.
40-50: Mesotrophic
having a moderate amount of nutrients. More organic matter is present, water is less clear.
50–70: Eutrophic
rich in nutrients and so supporting a dense plant population, the decomposition of which kills animal life by depriving it of oxygen.
70–100: Hypereutrophic
extremely rich in nutrients.
Drivers of Change
Certain activities on the land and characteristics of a watershed that have a negative impact on a pond's water quality and ecosystem health are called stressors. For example, a cranberry bog adjacent to a pond could be a stressor, as nutrients from fertilizers used to grow cranberries could be released into the pond. Similarly, golf courses may produce runoff carrying fertilizers and pesticides that travel to nearby ponds over the ground or through the groundwater.
Cape Cod Commission staff identified factors around a pond and assigned a score from zero to three. Factors that may have a detrimental impact on a pond were given a score of one, and factors that do not have a detrimental impact on ponds or may even help a pond to cope with a stressor, such as a centralized sewer system, were given a score of zero. Other more complex factors, such as the amount of impervious cover, were assigned a score on a scale. A list showing examples of characteristics that may impair a pond or help a pond cope with drivers of impairment is below.
| Stressor | Score |
| Adjacent to Cranberry Bog | 1 |
| Adjacent to Golf Course | 1 |
| % Developed within 300-ft | 0-3 |
| % Impervious cover within 100-ft | 0-3 |
| Centralized Sewer System | 0 |
| Nutrient Load | 0-3 |
Commission staff identified potential stressors using GIS data and our understanding of ponds, assigning a score to each pond. The scores were summed up, resulting in a cumulative stressor score for each pond, ranging from 2 (minimal stress) to 20 (highly stressed).
The most stressed ponds should be considered high priorities for monitoring and restoration activities, while the least stressed ponds should be considered for protection strategies. Listed below are the most stressed ponds on Cape Cod, followed by the least stressed ponds.
| Most Stressed Ponds | Score | |
| Long Pond | Yarmouth |
20 |
| Bucks Pond | Harwich | 20 |
| Wequaquet Lake | Barnstable | 20 |
| James Pond | Yarmouth | 19 |
| Jenkins Pond | Falmouth | 19 |
| Flax Pond | Bourne | 19 |
| Johns Pond | Mashpee | 19 |
| Dean's Pond | Mashpee | 19 |
| Lake Elizabeth | Barnstable | 18 |
| Peters Pond | Sandwich | 18 |
| Long Pond | Barnstable | 18 |
| Ashumet Pond | Mashpee | 18 |
| Least Stressed Ponds | Score | |
| Doanes Bog Pond | Wellfleet | 2 |
| Small Pond | Hyannis | 2 |
| Beccas Pond | Mashpee | 3 |
| Clapps Round Pond | Provincetown | 3 |
| Spectacle Pond | Wellfleet | 3 |
| Angel Mirror Pond | Falmouth | 3 |
| The Basin | Bourne | 3 |
| Miller Pond | Yarmouth | 3 |
| Cash Pond | Dennis | 3 |
| 1858 Bog | Brewster | 3 |
Interactive Map
This interactive map shows all of the ponds on Cape Cod ranked by their cumulative stressor score.
A possible way forward to manage the ponds based on their cumulative stressor score could include:
Minimally stressed (1-5): Develop a management plan to protect the ponds.
Some stress (6-10): Continue monitoring to ensure the pond does not further degrade while also developing a plan to protect the pond.
Stressed (11-15): Determine possible remediation projects that can be quickly implemented, such as stormwater management practices. Continue monitoring.
Highly stressed (16-20): Prioritize for mitigation. Identify and implement major rehabilitation strategies to reduce or remove stressors. Continue monitoring.
Hydrologic Response Unit
To help identify ponds where immediate, meaningful action may be taken, the hydrologic response unit (HRU) hotspots on a pond shore can be referenced to locate where stormwater management solutions should be considered.
The HRU tool generated the flow rate, the load of total suspended solids, total phosphorus, and total nitrogen. These stressors were included in the cumulative stressor score, and for this report were also mapped (Figure 1). Figure 1 (below) shows hotspots along pond shorelines where impervious surfaces (e.g., roads, boat ramps) and phosphorus loading hotspots intersect. These locations will need to be ground-truthed as the HRU tool does not take into consideration existing stormwater management practices.
Figure 1. Cape-wide HRU phosphorous loading hotspots where impervious surfaces are within 100 feet of the pond shore.
Takeaways
It’s important to note that there are many factors involved in a pond’s healthy ecosystem. The ponds with the highest scores aren’t necessarily the ponds with the highest trophic status. There are likely stressors that have not been quantified in the cumulative stressor score, as well as other variables that help a pond cope with stressors, such as short residence time and volume of a pond. Some of these variables that help a pond manage stressors were not included because the information is not available for all ponds; inclusion for some ponds and not others would skew the scores.
This study and the regional pond analysis have helped us understand that more data are needed, and more research needs to be done, including filling critical data gaps:
- Numerous ponds don’t have recorded maximum or average depths
- Calculate pond volumes and delineate watersheds so volume-to-watershed ratios can be determined for all ponds monitored
- Groundwater quality, specifically the concentration of total phosphorus
Regardless of pond health, there are easy-to-implement strategies that would benefit a pond. The HRU tool used in this project located phosphorus loading hotspots on pond shores (Hydrologic Response Unit tab (Figure 1)). Towns could reference this map to implement stormwater control measures.
For a deeper dive into this study, please see the Pond Characteristics Memo.
