While the requirement of "adjunct faculty" likely makes this too specific to have a study done looking at this, that doesn't mean we can't at least drawn some expected inferences from wider observed market forces and more general studies.
It's a "known issue" that the 30-hour requirement is resulting in some people having their work hours reduced so they don't count as full time. Back when the Affordable Care Act was not even passed yet there were employers - especially restaurants and other low-wage institutions - stating explicitly that this is what they'd be doing. So without a study, we'd explicitly expect this to be one effect of the law
As for studies seeking to quantify the effects, there are some, such as Effects of Federal Policy to Insure Young Adults:
Evidence from the 2010 Affordable Care Act’s
Dependent-Coverage Mandate. On page 23 we see:
Our data allow us to investigate the effects of the federal mandate
on whether young adults report working, whether they report working
full-time (30 hours or more), their weekly work hours, and their rate
of job turnover. We also examine the impact of the mandate on their
work schedule flexibility by evaluating the probability that young
adults have work hours that vary from week to week.
Our results,
starting with the first column of Table 7, show no statistically
significant evidence that the mandate affected the probability of
employment of young adults. Since the receipt of ESI is usually tied
to full-time work, we examined this measure next and find that the law
is associated with a reduced prevalence of full-time work by close to
2 percentage points (roughly 5.8 percent) during the period after
implementation began, relative to pre-ACA enactment. We also find
statistically significant evidence for a reduction in hours of work
(about a 3 percent reduction); these effects are statistically weaker
when we examine log hours as the dependent variable.
So this isn't a specific study to adjuncts, and this study specifically looks at young adults who aren't so likely to be adjunts, but without a specific study we are certainly permitted to assume that this is a real effect of the law - some people will see a cut in pay/hours so as to avoid having to be provideded benefits.
