Leaching nitrogen from residential households remains the single biggest threat to the water quality of Lagoon Pond, according to a recently completed water quality study. In a report delivered to the Lagoon Pond Association, its author found significant increases in nitrates entering the pond. The report is based on a series of water samplings conducted last summer.

Bruce Poole of SP Engineering Inc. and Vineyard Environmental Protection, the author, said yesterday: "The greatest threat to the water quality of the Lagoon Pond and its tributaries is an increase in housing and domestic residences." Mr. Poole's report offers suggestions for any future new or upgraded septic system construction.

His report comes at a time of growing concern about the future of the Lagoon Pond watershed, at a time when one developer is proposing either a luxury 18-hole golf course or a housing development in the pond watershed.

Mr. Poole began studying Lagoon Pond in 1983. His earliest studies of the Lagoon Pond identified serious pollution problems, many of which have since been resolved. His latest study warns that nutrient loading continues to increase despite the best efforts of Tisbury and Oak Bluffs town boards to manage growth.

He wrote in his report: "The summer was very dry so there were few rain events to transport nutrients and bacteria, therefore the water quality was good. The average nitrogen values for the tributaries and pond stations were all higher than the 1986 values, but the only significantly elevated nitrogen was the nitrates in Mud Creek, four hours after a one-inch rain event."

Mr. Poole said levels of nitrogen are on the increase elsewhere. "We conducted an abbreviated sampling schedule and analyzed the waters for fecal bacteria and nutrients. This included two periods of tributary sampling, one beach sampling and one groundwater sampling of three monitoring wells at the head of the Lagoon."

He wrote: "Homeowners within 200 feet of the shoreline have been made increasingly aware that their domestic wastewater must be adequately treated to protect the pond environment and that with advanced treatment each homeowner could remove 30 to 40 pounds of nitrogen from entering Lagoon Pond."

Mr. Poole said yesterday the rise in house construction is a big issue. "Visually you can note some of the houses on Weaver Lane or on Barnes Road. There is a rise in huge houses, guest houses and family houses," he said. "Even though they are not operated all year round, they are more of a threat to the pond because they put a large amount of nutrients in a very short time into the pond. It happens in the summer when the environment is much more susceptible to degradation."

Raising public awareness about the potential impact human waste can have on the pond is nothing new to Mr. Poole. In the early 1980s, Mr. Poole's studies of the pond were used by town boards to cut down on the number of failed septic systems emptying into the pond. Twenty years ago the Lagoon was considered a seriously troubled pond. Shellfish fisheries had collapsed and algae blooms were a problem.

Mr. Poole wrote: "Many old failed septic systems were found on Hines Point, Brush Pond and Upper Lagoon Pond. Untreated runoff was entering Mud Creek and creating a green algae mat. The Martha's Vineyard Hospital system was overloaded and washed out partially treated effluent during rain events and high tides."

In those years, residents were concerned about water quality and whether it was safe to go swimming in the pond. Mr. Poole said there were beach closings, and there was evidence of the die off of young shellfish at the head of the Lagoon. "It was all pointing to a rapid decline of the resource for humans and shellfish," he said.

Through the efforts of town boards, many failed septic systems were either repaired or upgraded. Mr. Poole said that from 1988 to 1994 the pond was basically productive. Mr. Poole said: "There weren't any major biological upsets."

But the issue of nutrient loading in the pond remains a serious concern. Among his recommendations to the Lagoon Pond Association, Mr. Poole said yesterday he thinks the monitoring wells he used in 1986 should be used again to track changes in the nitrogen loading all around the pond, especially in two areas. "We have seen two areas of Barnes Road and the Oklahoma Heights area that have shown increases in nitrogen loading in the last 20 years. We feel it is important to sample them annually to evaluate how housing construction is affecting Lagoon Pond water quality. At some point it may be necessary to impose regulations." That oversight would impact any new construction or expansion of existing homes. He said there is new technology available to homeowners that would cut down on nutrients.

Mr. Poole is promoting one nitrogen removal system that was installed off Barnes Road. This technology and others can be used to reduce the nutrients reaching the pond. He said if this new technology is used in the future for homes, the decline in water quality can be reversed.

William Wilcox, a water specialist with the Martha's Vineyard Commission, said he welcomes the report for the attention it draws to nutrient loading. "Any time you can draw public attention to the issues of nitrogen loading of our fragile coastal ponds, that is a good thing. I think it is good to upgrade septic systems around the Lagoon Pond or require new ones to use denitrification technology."

Mr. Wilcox said efforts by the town of Tisbury to put in a new wastewater treatment facility will help clean up the West Arm, where the readings are particularly high. He said, "Jo-ann Taylor [coastal planner for the commission] and her nitrogen analysis found that the Lagoon is being loaded at a rate close to its limit. That limit leads to algae blooms and declining eel grass beds. We've seen the symptoms in the system, and it is expected. Some summers are worse than others."

Richard Karney is director of the Martha's Vineyard Shellfish Group solar hatchery, which operates on the edge of Lagoon Pond. Mr. Karney said yesterday: "It doesn't surprise me that the nutrient enrichment of the pond is getting worse, and it is a problem."

Without referring specifically to the Down-Island Golf Club, for which he has worked as a consultant, Mr. Poole said he is in favor of golf courses in general. "I am in favor of open space. It can be recreational, it can be camp ground or golf, or farmland or open space for hiking. Domestic residences are a continuous source of nitrogen. The cumulative effect over time, I feel, is a great detriment. We have golf courses everywhere in my area of the state. They overlook salt marshes and lakes. I would see open space rather than 200 townhouses draining septage into a pristine surface water body."

Mr. Poole wrote: "The technical experts, aquaculturists and fishermen agree that Lagoon Pond is nitrogen sensitive and that excessive nitrogen loading, especially during the summer, can cause algal blooms and shellfish mortality. Since the pond does not need more nitrogen from any source, new projects in the DCPC should remove more nitrogen than they contribute." Mr. Poole noted: "The current nitrogen budget for Lagoon Pond does not take into account maximum build out, commercial business and school expansion. The nitrogen credit program should be an ongoing effort all around the ponds with homeowners and business doing their part to protect the water quality."